Nullability refinements in spring-webmvc

Includes revision of web.servlet.tags.form for non-null conventions.

Issue: SPR-15540

spring-context/src/main/java/org/springframework/ui/ModelMap.java

@@ -51,7 +51,7 @@ public class ModelMap extends LinkedHashMap<String, Object> {
 	 * under the supplied name.
 	 * @see #addAttribute(String, Object)
 	 */
-	public ModelMap(String attributeName, Object attributeValue) {
+	public ModelMap(String attributeName, @Nullable Object attributeValue) {
 		addAttribute(attributeName, attributeValue);
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/ModelAndView.java

@@ -280,12 +280,12 @@ public class ModelAndView {
 
 	/**
 	 * Add an attribute to the model.
-	 * @param attributeName name of the object to add to the model
-	 * @param attributeValue object to add to the model (never {@code null})
+	 * @param attributeName name of the object to add to the model (never {@code null})
+	 * @param attributeValue object to add to the model (can be {@code null})
 	 * @see ModelMap#addAttribute(String, Object)
 	 * @see #getModelMap()
 	 */
-	public ModelAndView addObject(String attributeName, Object attributeValue) {
+	public ModelAndView addObject(String attributeName, @Nullable Object attributeValue) {
 		getModelMap().addAttribute(attributeName, attributeValue);
 		return this;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/support/RequestDataValueProcessor.java

@@ -51,17 +51,17 @@ public interface RequestDataValueProcessor {
 	/**
 	 * Invoked when a form field value is rendered.
 	 * @param request the current request
-	 * @param name the form field name
+	 * @param name the form field name (if any)
 	 * @param value the form field value
 	 * @param type the form field type ("text", "hidden", etc.)
 	 * @return the form field value to use, possibly modified
 	 */
-	String processFormFieldValue(HttpServletRequest request, String name, String value, String type);
+	String processFormFieldValue(HttpServletRequest request, @Nullable String name, String value, String type);
 
 	/**
 	 * Invoked after all form fields have been rendered.
 	 * @param request the current request
-	 * @return additional hidden form fields to be added, or {@code null}
+	 * @return additional hidden form fields to be added, or {@code null} if none
 	 */
 	@Nullable
 	Map<String, String> getExtraHiddenFields(HttpServletRequest request);

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractCheckedElementTag.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,8 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Abstract base class to provide common methods for
  * implementing databinding-aware JSP tags for rendering an HTML '{@code input}'
@@ -36,7 +38,7 @@ public abstract class AbstractCheckedElementTag extends AbstractHtmlInputElement
 	 * '{@code input}' element as 'checked' if the supplied value matches the
 	 * bound value.
 	 */
-	protected void renderFromValue(Object value, TagWriter tagWriter) throws JspException {
+	protected void renderFromValue(@Nullable Object value, TagWriter tagWriter) throws JspException {
 		renderFromValue(value, value, tagWriter);
 	}
 
@@ -45,7 +47,9 @@ public abstract class AbstractCheckedElementTag extends AbstractHtmlInputElement
 	 * '{@code input}' element as 'checked' if the supplied value matches the
 	 * bound value.
 	 */
-	protected void renderFromValue(Object item, Object value, TagWriter tagWriter) throws JspException {
+	protected void renderFromValue(@Nullable Object item, @Nullable Object value, TagWriter tagWriter)
+			throws JspException {
+
 		String displayValue = convertToDisplayString(value);
 		tagWriter.writeAttribute("value", processFieldValue(getName(), displayValue, getInputType()));
 		if (isOptionSelected(value) || (value != item && isOptionSelected(item))) {
@@ -57,7 +61,7 @@ public abstract class AbstractCheckedElementTag extends AbstractHtmlInputElement
 	 * Determines whether the supplied value matched the selected value
 	 * through delegating to {@link SelectedValueComparator#isSelected}.
 	 */
-	private boolean isOptionSelected(Object value) throws JspException {
+	private boolean isOptionSelected(@Nullable Object value) throws JspException {
 		return SelectedValueComparator.isSelected(getBindStatus(), value);
 	}
 
@@ -77,8 +81,10 @@ public abstract class AbstractCheckedElementTag extends AbstractHtmlInputElement
 	 * Return a unique ID for the bound name within the current PageContext.
 	 */
 	@Override
+	@Nullable
 	protected String autogenerateId() throws JspException {
-		return TagIdGenerator.nextId(super.autogenerateId(), this.pageContext);
+		String id = super.autogenerateId();
+		return (id != null ? TagIdGenerator.nextId(id, this.pageContext) : null);
 	}
 
 

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractDataBoundFormElementTag.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -55,16 +55,19 @@ public abstract class AbstractDataBoundFormElementTag extends AbstractFormTag im
 	/**
 	 * The property path from the {@link FormTag#setModelAttribute form object}.
 	 */
+	@Nullable
 	private String path;
 
 	/**
 	 * The value of the '{@code id}' attribute.
 	 */
+	@Nullable
 	private String id;
 
 	/**
 	 * The {@link BindStatus} of this tag.
 	 */
+	@Nullable
 	private BindStatus bindStatus;
 
 
@@ -91,7 +94,7 @@ public abstract class AbstractDataBoundFormElementTag extends AbstractFormTag im
 	 * Note that the default value may not be valid for certain tags.
 	 */
 	@Override
-	public void setId(String id) {
+	public void setId(@Nullable String id) {
 		this.id = id;
 	}
 
@@ -99,6 +102,7 @@ public abstract class AbstractDataBoundFormElementTag extends AbstractFormTag im
 	 * Get the value of the '{@code id}' attribute.
 	 */
 	@Override
+	@Nullable
 	public String getId() {
 		return this.id;
 	}
@@ -179,6 +183,7 @@ public abstract class AbstractDataBoundFormElementTag extends AbstractFormTag im
 	 * Get the value of the nested path that may have been exposed by the
 	 * {@link NestedPathTag}.
 	 */
+	@Nullable
 	protected String getNestedPath() {
 		return (String) this.pageContext.getAttribute(NESTED_PATH_VARIABLE_NAME, PageContext.REQUEST_SCOPE);
 	}
@@ -225,7 +230,7 @@ public abstract class AbstractDataBoundFormElementTag extends AbstractFormTag im
 	 * Get a display String for the given value, converted by a PropertyEditor
 	 * that the BindStatus may have registered for the value's Class.
 	 */
-	protected String convertToDisplayString(Object value) throws JspException {
+	protected String convertToDisplayString(@Nullable Object value) throws JspException {
 		PropertyEditor editor = (value != null ? getBindStatus().findEditor(value.getClass()) : null);
 		return getDisplayString(value, editor);
 	}
@@ -234,10 +239,10 @@ public abstract class AbstractDataBoundFormElementTag extends AbstractFormTag im
 	 * Process the given form field through a {@link RequestDataValueProcessor}
 	 * instance if one is configured or otherwise returns the same value.
 	 */
-	protected final String processFieldValue(String name, String value, String type) {
+	protected final String processFieldValue(@Nullable String name, String value, String type) {
 		RequestDataValueProcessor processor = getRequestContext().getRequestDataValueProcessor();
 		ServletRequest request = this.pageContext.getRequest();
-		if (processor != null && (request instanceof HttpServletRequest)) {
+		if (processor != null && request instanceof HttpServletRequest) {
 			value = processor.processFormFieldValue((HttpServletRequest) request, name, value, type);
 		}
 		return value;

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractFormTag.java

@@ -45,7 +45,8 @@ public abstract class AbstractFormTag extends HtmlEscapingAwareTag {
 	 * Evaluate the supplied value for the supplied attribute name.
 	 * <p>The default implementation simply returns the given value as-is.
 	 */
-	protected Object evaluate(String attributeName, Object value) throws JspException {
+	@Nullable
+	protected Object evaluate(String attributeName, @Nullable Object value) throws JspException {
 		return value;
 	}
 
@@ -89,7 +90,7 @@ public abstract class AbstractFormTag extends HtmlEscapingAwareTag {
 	 * Get the display value of the supplied {@code Object}, HTML escaped
 	 * as required. This version is <strong>not</strong> {@link PropertyEditor}-aware.
 	 */
-	protected String getDisplayString(Object value) {
+	protected String getDisplayString(@Nullable Object value) {
 		return ValueFormatter.getDisplayString(value, isHtmlEscape());
 	}
 
@@ -99,7 +100,7 @@ public abstract class AbstractFormTag extends HtmlEscapingAwareTag {
 	 * {@link PropertyEditor} is not null then the {@link PropertyEditor} is used
 	 * to obtain the display value.
 	 */
-	protected String getDisplayString(Object value, PropertyEditor propertyEditor) {
+	protected String getDisplayString(@Nullable Object value, @Nullable PropertyEditor propertyEditor) {
 		return ValueFormatter.getDisplayString(value, propertyEditor, isHtmlEscape());
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractHtmlElementBodyTag.java

@@ -21,6 +21,8 @@ import javax.servlet.jsp.JspException;
 import javax.servlet.jsp.tagext.BodyContent;
 import javax.servlet.jsp.tagext.BodyTag;
 
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -35,8 +37,10 @@ import org.springframework.util.StringUtils;
 @SuppressWarnings("serial")
 public abstract class AbstractHtmlElementBodyTag extends AbstractHtmlElementTag implements BodyTag {
 
+	@Nullable
 	private BodyContent bodyContent;
 
+	@Nullable
 	private TagWriter tagWriter;
 
 
@@ -57,11 +61,12 @@ public abstract class AbstractHtmlElementBodyTag extends AbstractHtmlElementTag
 	 * If {@link #shouldRender rendering}, flush any buffered
 	 * {@link BodyContent} or, if no {@link BodyContent} is supplied,
 	 * {@link #renderDefaultContent render the default content}.
-	 * @return a {@link Tag#EVAL_PAGE} result
+	 * @return a {@link javax.servlet.jsp.tagext.Tag#EVAL_PAGE} result
 	 */
 	@Override
 	public int doEndTag() throws JspException {
 		if (shouldRender()) {
+			Assert.state(this.tagWriter != null, "No TagWriter set");
 			if (this.bodyContent != null && StringUtils.hasText(this.bodyContent.getString())) {
 				renderFromBodyContent(this.bodyContent, this.tagWriter);
 			}
@@ -79,7 +84,7 @@ public abstract class AbstractHtmlElementBodyTag extends AbstractHtmlElementTag
 	 * override this to add additional content to the output.
 	 */
 	protected void renderFromBodyContent(BodyContent bodyContent, TagWriter tagWriter) throws JspException {
-		flushBufferedBodyContent(this.bodyContent);
+		flushBufferedBodyContent(bodyContent);
 	}
 
 	/**

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractHtmlElementTag.java

@@ -21,6 +21,7 @@ import java.util.Map;
 import javax.servlet.jsp.JspException;
 import javax.servlet.jsp.tagext.DynamicAttributes;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -76,40 +77,58 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	public static final String ONKEYDOWN_ATTRIBUTE = "onkeydown";
 
 
+	@Nullable
 	private String cssClass;
 
+	@Nullable
 	private String cssErrorClass;
 
+	@Nullable
 	private String cssStyle;
 
+	@Nullable
 	private String lang;
 
+	@Nullable
 	private String title;
 
+	@Nullable
 	private String dir;
 
+	@Nullable
 	private String tabindex;
 
+	@Nullable
 	private String onclick;
 
+	@Nullable
 	private String ondblclick;
 
+	@Nullable
 	private String onmousedown;
 
+	@Nullable
 	private String onmouseup;
 
+	@Nullable
 	private String onmouseover;
 
+	@Nullable
 	private String onmousemove;
 
+	@Nullable
 	private String onmouseout;
 
+	@Nullable
 	private String onkeypress;
 
+	@Nullable
 	private String onkeyup;
 
+	@Nullable
 	private String onkeydown;
 
+	@Nullable
 	private Map<String, Object> dynamicAttributes;
 
 
@@ -125,6 +144,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code class}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getCssClass() {
 		return this.cssClass;
 	}
@@ -141,6 +161,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * The CSS class to use when the field bound to a particular tag has errors.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getCssErrorClass() {
 		return this.cssErrorClass;
 	}
@@ -157,6 +178,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code style}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getCssStyle() {
 		return this.cssStyle;
 	}
@@ -173,6 +195,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code lang}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getLang() {
 		return this.lang;
 	}
@@ -189,6 +212,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code title}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getTitle() {
 		return this.title;
 	}
@@ -205,6 +229,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code dir}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getDir() {
 		return this.dir;
 	}
@@ -221,6 +246,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code tabindex}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getTabindex() {
 		return this.tabindex;
 	}
@@ -237,6 +263,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onclick}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnclick() {
 		return this.onclick;
 	}
@@ -253,6 +280,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code ondblclick}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOndblclick() {
 		return this.ondblclick;
 	}
@@ -269,6 +297,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onmousedown}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnmousedown() {
 		return this.onmousedown;
 	}
@@ -285,6 +314,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onmouseup}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnmouseup() {
 		return this.onmouseup;
 	}
@@ -301,6 +331,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onmouseover}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnmouseover() {
 		return this.onmouseover;
 	}
@@ -317,6 +348,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onmousemove}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnmousemove() {
 		return this.onmousemove;
 	}
@@ -332,6 +364,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onmouseout}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnmouseout() {
 		return this.onmouseout;
 	}
@@ -348,6 +381,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onkeypress}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnkeypress() {
 		return this.onkeypress;
 	}
@@ -364,6 +398,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onkeyup}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnkeyup() {
 		return this.onkeyup;
 	}
@@ -380,6 +415,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * Get the value of the '{@code onkeydown}' attribute.
 	 * May be a runtime expression.
 	 */
+	@Nullable
 	protected String getOnkeydown() {
 		return this.onkeydown;
 	}
@@ -387,6 +423,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	/**
 	 * Get the map of dynamic attributes.
 	 */
+	@Nullable
 	protected Map<String, Object> getDynamicAttributes() {
 		return this.dynamicAttributes;
 	}
@@ -395,7 +432,7 @@ public abstract class AbstractHtmlElementTag extends AbstractDataBoundFormElemen
 	 * {@inheritDoc}
 	 */
 	@Override
-	public void setDynamicAttribute(String uri, String localName, Object value ) throws JspException {
+	public void setDynamicAttribute(String uri, String localName, Object value) throws JspException {
 		if (this.dynamicAttributes == null) {
 			this.dynamicAttributes = new HashMap<>();
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractHtmlInputElementTag.java

 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,8 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Base class for databinding-aware JSP tags that render HTML form input element.
  *
@@ -63,12 +65,16 @@ public abstract class AbstractHtmlInputElementTag extends AbstractHtmlElementTag
 	public static final String READONLY_ATTRIBUTE = "readonly";
 
 
+	@Nullable
 	private String onfocus;
 
+	@Nullable
 	private String onblur;
 
+	@Nullable
 	private String onchange;
 
+	@Nullable
 	private String accesskey;
 
 	private boolean disabled;
@@ -87,6 +93,7 @@ public abstract class AbstractHtmlInputElementTag extends AbstractHtmlElementTag
 	/**
 	 * Get the value of the '{@code onfocus}' attribute.
 	 */
+	@Nullable
 	protected String getOnfocus() {
 		return this.onfocus;
 	}
@@ -102,6 +109,7 @@ public abstract class AbstractHtmlInputElementTag extends AbstractHtmlElementTag
 	/**
 	 * Get the value of the '{@code onblur}' attribute.
 	 */
+	@Nullable
 	protected String getOnblur() {
 		return this.onblur;
 	}
@@ -117,6 +125,7 @@ public abstract class AbstractHtmlInputElementTag extends AbstractHtmlElementTag
 	/**
 	 * Get the value of the '{@code onchange}' attribute.
 	 */
+	@Nullable
 	protected String getOnchange() {
 		return this.onchange;
 	}
@@ -132,6 +141,7 @@ public abstract class AbstractHtmlInputElementTag extends AbstractHtmlElementTag
 	/**
 	 * Get the value of the '{@code accesskey}' attribute.
 	 */
+	@Nullable
 	protected String getAccesskey() {
 		return this.accesskey;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractMultiCheckedElementTag.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,7 @@ import javax.servlet.jsp.JspException;
 
 import org.springframework.beans.BeanWrapper;
 import org.springframework.beans.PropertyAccessorFactory;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -50,17 +51,20 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 	 * The {@link java.util.Collection}, {@link java.util.Map} or array of objects
 	 * used to generate the '{@code input type="checkbox/radio"}' tags.
 	 */
+	@Nullable
 	private Object items;
 
 	/**
 	 * The name of the property mapped to the '{@code value}' attribute
 	 * of the '{@code input type="checkbox/radio"}' tag.
 	 */
+	@Nullable
 	private String itemValue;
 
 	/**
 	 * The value to be displayed as part of the '{@code input type="checkbox/radio"}' tag.
 	 */
+	@Nullable
 	private String itemLabel;
 
 	/**
@@ -71,6 +75,7 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 	/**
 	 * Delimiter to use between each '{@code input type="checkbox/radio"}' tags.
 	 */
+	@Nullable
 	private String delimiter;
 
 
@@ -89,6 +94,7 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 	 * Get the {@link java.util.Collection}, {@link java.util.Map} or array of objects
 	 * used to generate the '{@code input type="checkbox/radio"}' tags.
 	 */
+	@Nullable
 	protected Object getItems() {
 		return this.items;
 	}
@@ -107,6 +113,7 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 	 * Get the name of the property mapped to the '{@code value}' attribute
 	 * of the '{@code input type="checkbox/radio"}' tag.
 	 */
+	@Nullable
 	protected String getItemValue() {
 		return this.itemValue;
 	}
@@ -125,6 +132,7 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 	 * Get the value to be displayed as part of the
 	 * '{@code input type="checkbox/radio"}' tag.
 	 */
+	@Nullable
 	protected String getItemLabel() {
 		return this.itemLabel;
 	}
@@ -142,6 +150,7 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 	 * Return the delimiter to be used between each
 	 * '{@code input type="radio"}' tag.
 	 */
+	@Nullable
 	public String getDelimiter() {
 		return this.delimiter;
 	}
@@ -236,8 +245,8 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 		return SKIP_BODY;
 	}
 
-	private void writeObjectEntry(TagWriter tagWriter, String valueProperty,
-			String labelProperty, Object item, int itemIndex) throws JspException {
+	private void writeObjectEntry(TagWriter tagWriter, @Nullable String valueProperty,
+			@Nullable String labelProperty, Object item, int itemIndex) throws JspException {
 
 		BeanWrapper wrapper = PropertyAccessorFactory.forBeanPropertyAccess(item);
 		Object renderValue;
@@ -254,8 +263,8 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 		writeElementTag(tagWriter, item, renderValue, renderLabel, itemIndex);
 	}
 
-	private void writeMapEntry(TagWriter tagWriter, String valueProperty,
-			String labelProperty, Map.Entry<?, ?> entry, int itemIndex) throws JspException {
+	private void writeMapEntry(TagWriter tagWriter, @Nullable String valueProperty,
+			@Nullable String labelProperty, Map.Entry<?, ?> entry, int itemIndex) throws JspException {
 
 		Object mapKey = entry.getKey();
 		Object mapValue = entry.getValue();
@@ -268,8 +277,8 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 		writeElementTag(tagWriter, mapKey, renderValue, renderLabel, itemIndex);
 	}
 
-	private void writeElementTag(TagWriter tagWriter, Object item, Object value, Object label, int itemIndex)
-			throws JspException {
+	private void writeElementTag(TagWriter tagWriter, Object item, @Nullable Object value,
+			@Nullable Object label, int itemIndex) throws JspException {
 
 		tagWriter.startTag(getElement());
 		if (itemIndex > 0) {
@@ -280,6 +289,7 @@ public abstract class AbstractMultiCheckedElementTag extends AbstractCheckedElem
 		}
 		tagWriter.startTag("input");
 		String id = resolveId();
+		Assert.state(id != null, "Attribute 'id' is required");
 		writeOptionalAttribute(tagWriter, "id", id);
 		writeOptionalAttribute(tagWriter, "name", getName());
 		writeOptionalAttributes(tagWriter);

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/AbstractSingleCheckedElementTag.java

@@ -18,6 +18,9 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
 /**
  * Abstract base class to provide common methods for implementing
  * databinding-aware JSP tags for rendering a <i>single</i>
@@ -33,11 +36,13 @@ public abstract class AbstractSingleCheckedElementTag extends AbstractCheckedEle
 	/**
 	 * The value of the '{@code value}' attribute.
 	 */
+	@Nullable
 	private Object value;
 
 	/**
 	 * The value of the '{@code label}' attribute.
 	 */
+	@Nullable
 	private Object label;
 
 
@@ -52,6 +57,7 @@ public abstract class AbstractSingleCheckedElementTag extends AbstractCheckedEle
 	/**
 	 * Get the value of the '{@code value}' attribute.
 	 */
+	@Nullable
 	protected Object getValue() {
 		return this.value;
 	}
@@ -67,6 +73,7 @@ public abstract class AbstractSingleCheckedElementTag extends AbstractCheckedEle
 	/**
 	 * Get the value of the '{@code label}' attribute.
 	 */
+	@Nullable
 	protected Object getLabel() {
 		return this.label;
 	}
@@ -89,6 +96,7 @@ public abstract class AbstractSingleCheckedElementTag extends AbstractCheckedEle
 
 		Object resolvedLabel = evaluate("label", getLabel());
 		if (resolvedLabel != null) {
+			Assert.state(id != null, "Label id is required");
 			tagWriter.startTag("label");
 			tagWriter.writeAttribute("for", id);
 			tagWriter.appendValue(convertToDisplayString(resolvedLabel));

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/ButtonTag.java

@@ -18,6 +18,8 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.web.servlet.support.RequestDataValueProcessor;
 
 /**
@@ -77,10 +79,13 @@ public class ButtonTag extends AbstractHtmlElementTag {
 	public static final String DISABLED_ATTRIBUTE = "disabled";
 
 
+	@Nullable
 	private TagWriter tagWriter;
 
+	@Nullable
 	private String name;
 
+	@Nullable
 	private String value;
 
 	private boolean disabled;
@@ -97,6 +102,7 @@ public class ButtonTag extends AbstractHtmlElementTag {
 	 * Set the value of the '{@code name}' attribute.
 	 */
 	@Override
+	@Nullable
 	public String getName() {
 		return this.name;
 	}
@@ -104,13 +110,14 @@ public class ButtonTag extends AbstractHtmlElementTag {
 	/**
 	 * Set the value of the '{@code value}' attribute.
 	 */
-	public void setValue(String value) {
+	public void setValue(@Nullable String value) {
 		this.value = value;
 	}
 
 	/**
 	 * Get the value of the '{@code value}' attribute.
 	 */
+	@Nullable
 	public String getValue() {
 		return this.value;
 	}
@@ -150,7 +157,7 @@ public class ButtonTag extends AbstractHtmlElementTag {
 	 * when the value is written.
 	 */
 	protected void writeValue(TagWriter tagWriter) throws JspException {
-		String valueToUse = (getValue() != null) ? getValue() : getDefaultValue();
+		String valueToUse = (getValue() != null ? getValue() : getDefaultValue());
 		tagWriter.writeAttribute("value", processFieldValue(getName(), valueToUse, getType()));
 	}
 
@@ -176,6 +183,7 @@ public class ButtonTag extends AbstractHtmlElementTag {
 	 */
 	@Override
 	public int doEndTag() throws JspException {
+		Assert.state(this.tagWriter != null, "No TagWriter set");
 		this.tagWriter.endTag();
 		return EVAL_PAGE;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/ErrorsTag.java

@@ -23,6 +23,7 @@ import javax.servlet.jsp.JspException;
 import javax.servlet.jsp.PageContext;
 import javax.servlet.jsp.tagext.BodyTag;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -209,6 +210,7 @@ public class ErrorsTag extends AbstractHtmlElementBodyTag implements BodyTag {
 	/**
 	 * Stores any value that existed in the 'errors messages' before the tag was started.
 	 */
+	@Nullable
 	private Object oldMessages;
 
 	private boolean errorMessagesWereExposed;
@@ -270,6 +272,7 @@ public class ErrorsTag extends AbstractHtmlElementBodyTag implements BodyTag {
 	 * is not a validate attribute for the '{@code span}' element.
 	 */
 	@Override
+	@Nullable
 	protected String getName() throws JspException {
 		return null;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/FormTag.java

@@ -28,6 +28,8 @@ import javax.servlet.jsp.PageContext;
 import org.springframework.beans.PropertyAccessor;
 import org.springframework.core.Conventions;
 import org.springframework.http.HttpMethod;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -288,33 +290,44 @@ public class FormTag extends AbstractHtmlElementTag {
 	private static final String TYPE_ATTRIBUTE = "type";
 
 
+	@Nullable
 	private TagWriter tagWriter;
 
 	private String modelAttribute = DEFAULT_COMMAND_NAME;
 
+	@Nullable
 	private String name;
 
+	@Nullable
 	private String action;
 
+	@Nullable
 	private String servletRelativeAction;
 
 	private String method = DEFAULT_METHOD;
 
+	@Nullable
 	private String target;
 
+	@Nullable
 	private String enctype;
 
+	@Nullable
 	private String acceptCharset;
 
+	@Nullable
 	private String onsubmit;
 
+	@Nullable
 	private String onreset;
 
+	@Nullable
 	private String autocomplete;
 
 	private String methodParam = DEFAULT_METHOD_PARAM;
 
 	/** Caching a previous nested path, so that it may be reset. */
+	@Nullable
 	private String previousNestedPath;
 
 
@@ -347,6 +360,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	 * Get the value of the '{@code name}' attribute.
 	 */
 	@Override
+	@Nullable
 	protected String getName() throws JspException {
 		return this.name;
 	}
@@ -355,13 +369,14 @@ public class FormTag extends AbstractHtmlElementTag {
 	 * Set the value of the '{@code action}' attribute.
 	 * <p>May be a runtime expression.
 	 */
-	public void setAction(String action) {
+	public void setAction(@Nullable String action) {
 		this.action = (action != null ? action : "");
 	}
 
 	/**
 	 * Get the value of the '{@code action}' attribute.
 	 */
+	@Nullable
 	protected String getAction() {
 		return this.action;
 	}
@@ -372,14 +387,15 @@ public class FormTag extends AbstractHtmlElementTag {
 	 * <p>May be a runtime expression.
 	 * @since 3.2.3
 	 */
-	public void setServletRelativeAction(String servletRelativeAction) {
-		this.servletRelativeAction = (servletRelativeAction != null ? servletRelativeAction : "");
+	public void setServletRelativeAction(@Nullable String servletRelativeAction) {
+		this.servletRelativeAction = servletRelativeAction;
 	}
 
 	/**
 	 * Get the servlet-relative value of the '{@code action}' attribute.
 	 * @since 3.2.3
 	 */
+	@Nullable
 	protected String getServletRelativeAction() {
 		return this.servletRelativeAction;
 	}
@@ -410,6 +426,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Get the value of the '{@code target}' attribute.
 	 */
+	@Nullable
 	public String getTarget() {
 		return this.target;
 	}
@@ -425,6 +442,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Get the value of the '{@code enctype}' attribute.
 	 */
+	@Nullable
 	protected String getEnctype() {
 		return this.enctype;
 	}
@@ -440,6 +458,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Get the value of the '{@code acceptCharset}' attribute.
 	 */
+	@Nullable
 	protected String getAcceptCharset() {
 		return this.acceptCharset;
 	}
@@ -455,6 +474,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Get the value of the '{@code onsubmit}' attribute.
 	 */
+	@Nullable
 	protected String getOnsubmit() {
 		return this.onsubmit;
 	}
@@ -470,6 +490,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Get the value of the '{@code onreset}' attribute.
 	 */
+	@Nullable
 	protected String getOnreset() {
 		return this.onreset;
 	}
@@ -485,6 +506,7 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Get the value of the '{@code autocomplete}' attribute.
 	 */
+	@Nullable
 	protected String getAutocomplete() {
 		return this.autocomplete;
 	}
@@ -670,6 +692,7 @@ public class FormTag extends AbstractHtmlElementTag {
 		if (processor != null && request instanceof HttpServletRequest) {
 			writeHiddenFields(processor.getExtraHiddenFields((HttpServletRequest) request));
 		}
+		Assert.state(this.tagWriter != null, "No TagWriter set");
 		this.tagWriter.endTag();
 		return EVAL_PAGE;
 	}
@@ -677,8 +700,9 @@ public class FormTag extends AbstractHtmlElementTag {
 	/**
 	 * Writes the given values as hidden fields.
 	 */
-	private void writeHiddenFields(Map<String, String> hiddenFields) throws JspException {
+	private void writeHiddenFields(@Nullable Map<String, String> hiddenFields) throws JspException {
 		if (!CollectionUtils.isEmpty(hiddenFields)) {
+			Assert.state(this.tagWriter != null, "No TagWriter set");
 			this.tagWriter.appendValue("<div>\n");
 			for (String name : hiddenFields.keySet()) {
 				this.tagWriter.appendValue("<input type=\"hidden\" ");

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/InputTag.java

@@ -16,8 +16,11 @@
 
 package org.springframework.web.servlet.tags.form;
 
+import java.util.Map;
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
+
 /**
  * The {@code <input>} tag renders an HTML 'input' tag with type 'text' using
  * the bound value.
@@ -241,19 +244,22 @@ public class InputTag extends AbstractHtmlInputElementTag {
 
 	public static final String ONSELECT_ATTRIBUTE = "onselect";
 
-	public static final String READONLY_ATTRIBUTE = "readonly";
-
 	public static final String AUTOCOMPLETE_ATTRIBUTE = "autocomplete";
 
 
+	@Nullable
 	private String size;
 
+	@Nullable
 	private String maxlength;
 
+	@Nullable
 	private String alt;
 
+	@Nullable
 	private String onselect;
 
+	@Nullable
 	private String autocomplete;
 
 
@@ -268,6 +274,7 @@ public class InputTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code size}' attribute.
 	 */
+	@Nullable
 	protected String getSize() {
 		return this.size;
 	}
@@ -283,6 +290,7 @@ public class InputTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code maxlength}' attribute.
 	 */
+	@Nullable
 	protected String getMaxlength() {
 		return this.maxlength;
 	}
@@ -298,6 +306,7 @@ public class InputTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code alt}' attribute.
 	 */
+	@Nullable
 	protected String getAlt() {
 		return this.alt;
 	}
@@ -313,6 +322,7 @@ public class InputTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code onselect}' attribute.
 	 */
+	@Nullable
 	protected String getOnselect() {
 		return this.onselect;
 	}
@@ -328,6 +338,7 @@ public class InputTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code autocomplete}' attribute.
 	 */
+	@Nullable
 	protected String getAutocomplete() {
 		return this.autocomplete;
 	}
@@ -343,7 +354,8 @@ public class InputTag extends AbstractHtmlInputElementTag {
 		tagWriter.startTag("input");
 
 		writeDefaultAttributes(tagWriter);
-		if (!hasDynamicTypeAttribute()) {
+		Map<String, Object> attributes = getDynamicAttributes();
+		if (attributes == null || !attributes.containsKey("type")) {
 			tagWriter.writeAttribute("type", getType());
 		}
 		writeValue(tagWriter);
@@ -359,10 +371,6 @@ public class InputTag extends AbstractHtmlInputElementTag {
 		return SKIP_BODY;
 	}
 
-	private boolean hasDynamicTypeAttribute() {
-		return getDynamicAttributes() != null && getDynamicAttributes().containsKey("type");
-	}
-
 	/**
 	 * Writes the '{@code value}' attribute to the supplied {@link TagWriter}.
 	 * Subclasses may choose to override this implementation to control exactly
@@ -370,7 +378,14 @@ public class InputTag extends AbstractHtmlInputElementTag {
 	 */
 	protected void writeValue(TagWriter tagWriter) throws JspException {
 		String value = getDisplayString(getBoundValue(), getPropertyEditor());
-		String type = hasDynamicTypeAttribute() ? (String) getDynamicAttributes().get("type") : getType();
+		String type = null;
+		Map<String, Object> attributes = getDynamicAttributes();
+		if (attributes != null) {
+			type = (String) getDynamicAttributes().get("type");
+		}
+		if (type == null) {
+			type = getType();
+		}
 		tagWriter.writeAttribute("value", processFieldValue(getName(), value, type));
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/LabelTag.java

@@ -18,6 +18,7 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
@@ -190,21 +191,21 @@ public class LabelTag extends AbstractHtmlElementTag {
 	 * The {@link TagWriter} instance being used.
 	 * <p>Stored so we can close the tag on {@link #doEndTag()}.
 	 */
+	@Nullable
 	private TagWriter tagWriter;
 
 	/**
 	 * The value of the '{@code for}' attribute.
 	 */
+	@Nullable
 	private String forId;
 
 
 	/**
 	 * Set the value of the '{@code for}' attribute.
 	 * <p>Defaults to the value of {@link #getPath}; may be a runtime expression.
-	 * @throws IllegalArgumentException if the supplied value is {@code null}
 	 */
 	public void setFor(String forId) {
-		Assert.notNull(forId, "'forId' must not be null");
 		this.forId = forId;
 	}
 
@@ -212,7 +213,8 @@ public class LabelTag extends AbstractHtmlElementTag {
 	 * Get the value of the '{@code id}' attribute.
 	 * <p>May be a runtime expression.
 	 */
-	public String getFor() {
+	@Nullable
+	protected String getFor() {
 		return this.forId;
 	}
 
@@ -239,6 +241,7 @@ public class LabelTag extends AbstractHtmlElementTag {
 	 * @return the value for the HTML '{@code name}' attribute
 	 */
 	@Override
+	@Nullable
 	protected String getName() throws JspException {
 		// This also suppresses the 'id' attribute (which is okay for a <label/>)
 		return null;
@@ -273,6 +276,7 @@ public class LabelTag extends AbstractHtmlElementTag {
 	 */
 	@Override
 	public int doEndTag() throws JspException {
+		Assert.state(this.tagWriter != null, "No TagWriter set");
 		this.tagWriter.endTag();
 		return EVAL_PAGE;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/OptionTag.java

 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,7 +20,7 @@ import javax.servlet.jsp.JspException;
 import javax.servlet.jsp.tagext.BodyContent;
 import javax.servlet.jsp.tagext.BodyTag;
 
-import org.springframework.util.Assert;
+import org.springframework.lang.Nullable;
 import org.springframework.web.servlet.support.BindStatus;
 import org.springframework.web.util.TagUtils;
 
@@ -228,15 +228,19 @@ public class OptionTag extends AbstractHtmlElementBodyTag implements BodyTag {
 	/**
 	 * The 'value' attribute of the rendered HTML {@code <option>} tag.
 	 */
+	@Nullable
 	private Object value;
 
 	/**
 	 * The text body of the rendered HTML {@code <option>} tag.
 	 */
+	@Nullable
 	private String label;
 
+	@Nullable
 	private Object oldValue;
 
+	@Nullable
 	private Object oldDisplayValue;
 
 	private boolean disabled;
@@ -252,6 +256,7 @@ public class OptionTag extends AbstractHtmlElementBodyTag implements BodyTag {
 	/**
 	 * Get the 'value' attribute of the rendered HTML {@code <option>} tag.
 	 */
+	@Nullable
 	protected Object getValue() {
 		return this.value;
 	}
@@ -275,13 +280,13 @@ public class OptionTag extends AbstractHtmlElementBodyTag implements BodyTag {
 	 * <p>May be a runtime expression.
 	 */
 	public void setLabel(String label) {
-		Assert.notNull(label, "'label' must not be null");
 		this.label = label;
 	}
 
 	/**
 	 * Get the text body of the rendered HTML {@code <option>} tag.
 	 */
+	@Nullable
 	protected String getLabel() {
 		return this.label;
 	}
@@ -365,8 +370,8 @@ public class OptionTag extends AbstractHtmlElementBodyTag implements BodyTag {
 	}
 
 	/**
-	 * Returns the value of the label for this '{@code option}' element.
-	 * If the {@link #setLabel label} property is set then the resolved value
+	 * Return the value of the label for this '{@code option}' element.
+	 * <p>If the {@link #setLabel label} property is set then the resolved value
 	 * of that property is used, otherwise the value of the {@code resolvedValue}
 	 * argument is used.
 	 */
@@ -388,6 +393,7 @@ public class OptionTag extends AbstractHtmlElementBodyTag implements BodyTag {
 		return SelectedValueComparator.isSelected(getBindStatus(), resolvedValue);
 	}
 
+	@Nullable
 	private Object resolveValue() throws JspException {
 		return evaluate(VALUE_VARIABLE_NAME, getValue());
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/OptionWriter.java

@@ -23,6 +23,7 @@ import javax.servlet.jsp.JspException;
 
 import org.springframework.beans.BeanWrapper;
 import org.springframework.beans.PropertyAccessorFactory;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 import org.springframework.web.servlet.support.BindStatus;
@@ -92,15 +93,17 @@ class OptionWriter {
 
 	private final BindStatus bindStatus;
 
+	@Nullable
 	private final String valueProperty;
 
+	@Nullable
 	private final String labelProperty;
 
 	private final boolean htmlEscape;
 
 
 	/**
-	 * Creates a new {@code OptionWriter} for the supplied {@code objectSource}.
+	 * Create a new {@code OptionWriter} for the supplied {@code objectSource}.
 	 * @param optionSource the source of the {@code options} (never {@code null})
 	 * @param bindStatus the {@link BindStatus} for the bound value (never {@code null})
 	 * @param valueProperty the name of the property used to render {@code option} values
@@ -108,8 +111,8 @@ class OptionWriter {
 	 * @param labelProperty the name of the property used to render {@code option} labels
 	 * (optional)
 	 */
-	public OptionWriter(
-			Object optionSource, BindStatus bindStatus, String valueProperty, String labelProperty, boolean htmlEscape) {
+	public OptionWriter(Object optionSource, BindStatus bindStatus,
+			@Nullable String valueProperty, @Nullable String labelProperty, boolean htmlEscape) {
 
 		Assert.notNull(optionSource, "'optionSource' must not be null");
 		Assert.notNull(bindStatus, "'bindStatus' must not be null");
@@ -145,7 +148,7 @@ class OptionWriter {
 	}
 
 	/**
-	 * Renders the inner '{@code option}' tags using the {@link #optionSource}.
+	 * Render the inner '{@code option}' tags using the {@link #optionSource}.
 	 * @see #doRenderFromCollection(java.util.Collection, TagWriter)
 	 */
 	private void renderFromArray(TagWriter tagWriter) throws JspException {
@@ -153,7 +156,7 @@ class OptionWriter {
 	}
 
 	/**
-	 * Renders the inner '{@code option}' tags using the supplied
+	 * Render the inner '{@code option}' tags using the supplied
 	 * {@link Map} as the source.
 	 * @see #renderOption(TagWriter, Object, Object, Object)
 	 */
@@ -173,7 +176,7 @@ class OptionWriter {
 	}
 
 	/**
-	 * Renders the inner '{@code option}' tags using the {@link #optionSource}.
+	 * Render the inner '{@code option}' tags using the {@link #optionSource}.
 	 * @see #doRenderFromCollection(java.util.Collection, TagWriter)
 	 */
 	private void renderFromCollection(TagWriter tagWriter) throws JspException {
@@ -181,7 +184,7 @@ class OptionWriter {
 	}
 
 	/**
-	 * Renders the inner '{@code option}' tags using the {@link #optionSource}.
+	 * Render the inner '{@code option}' tags using the {@link #optionSource}.
 	 * @see #doRenderFromCollection(java.util.Collection, TagWriter)
 	 */
 	private void renderFromEnum(TagWriter tagWriter) throws JspException {
@@ -189,7 +192,7 @@ class OptionWriter {
 	}
 
 	/**
-	 * Renders the inner '{@code option}' tags using the supplied {@link Collection} of
+	 * Render the inner '{@code option}' tags using the supplied {@link Collection} of
 	 * objects as the source. The value of the {@link #valueProperty} field is used
 	 * when rendering the '{@code value}' of the '{@code option}' and the value of the
 	 * {@link #labelProperty} property is used when rendering the label.
@@ -213,10 +216,12 @@ class OptionWriter {
 	}
 
 	/**
-	 * Renders an HTML '{@code option}' with the supplied value and label. Marks the
+	 * Render an HTML '{@code option}' with the supplied value and label. Marks the
 	 * value as 'selected' if either the item itself or its value match the bound value.
 	 */
-	private void renderOption(TagWriter tagWriter, Object item, Object value, Object label) throws JspException {
+	private void renderOption(TagWriter tagWriter, Object item, @Nullable Object value, @Nullable Object label)
+			throws JspException {
+
 		tagWriter.startTag("option");
 		writeCommonAttributes(tagWriter);
 
@@ -239,17 +244,17 @@ class OptionWriter {
 	}
 
 	/**
-	 * Determines the display value of the supplied {@code Object},
+	 * Determine the display value of the supplied {@code Object},
 	 * HTML-escaped as required.
 	 */
-	private String getDisplayString(Object value) {
+	private String getDisplayString(@Nullable Object value) {
 		PropertyEditor editor = (value != null ? this.bindStatus.findEditor(value.getClass()) : null);
 		return ValueFormatter.getDisplayString(value, editor, this.htmlEscape);
 	}
 
 	/**
 	 * Process the option value before it is written.
-	 * The default implementation simply returns the same value unchanged.
+	 * <p>The default implementation simply returns the same value unchanged.
 	 */
 	protected String processOptionValue(String resolvedValue) {
 		return resolvedValue;
@@ -257,9 +262,9 @@ class OptionWriter {
 
 	/**
 	 * Determine whether the supplied values matched the selected value.
-	 * Delegates to {@link SelectedValueComparator#isSelected}.
+	 * <p>Delegates to {@link SelectedValueComparator#isSelected}.
 	 */
-	private boolean isOptionSelected(Object resolvedValue) {
+	private boolean isOptionSelected(@Nullable Object resolvedValue) {
 		return SelectedValueComparator.isSelected(this.bindStatus, resolvedValue);
 	}
 
@@ -271,7 +276,7 @@ class OptionWriter {
 	}
 
 	/**
-	 * Writes default attributes configured to the supplied {@link TagWriter}.
+	 * Write default attributes configured to the supplied {@link TagWriter}.
 	 */
 	protected void writeCommonAttributes(TagWriter tagWriter) throws JspException {
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/OptionsTag.java

 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -196,18 +197,21 @@ public class OptionsTag extends AbstractHtmlElementTag {
 	 * The {@link java.util.Collection}, {@link java.util.Map} or array of
 	 * objects used to generate the inner '{@code option}' tags.
 	 */
+	@Nullable
 	private Object items;
 
 	/**
 	 * The name of the property mapped to the '{@code value}' attribute
 	 * of the '{@code option}' tag.
 	 */
+	@Nullable
 	private String itemValue;
 
 	/**
 	 * The name of the property mapped to the inner text of the
 	 * '{@code option}' tag.
 	 */
+	@Nullable
 	private String itemLabel;
 
 	private boolean disabled;
@@ -229,6 +233,7 @@ public class OptionsTag extends AbstractHtmlElementTag {
 	 * of objects used to generate the inner '{@code option}' tags.
 	 * <p>Typically a runtime expression.
 	 */
+	@Nullable
 	protected Object getItems() {
 		return this.items;
 	}
@@ -248,6 +253,7 @@ public class OptionsTag extends AbstractHtmlElementTag {
 	 * Return the name of the property mapped to the '{@code value}'
 	 * attribute of the '{@code option}' tag.
 	 */
+	@Nullable
 	protected String getItemValue() {
 		return this.itemValue;
 	}
@@ -265,6 +271,7 @@ public class OptionsTag extends AbstractHtmlElementTag {
 	 * Get the name of the property mapped to the label (inner text) of the
 	 * '{@code option}' tag.
 	 */
+	@Nullable
 	protected String getItemLabel() {
 		return this.itemLabel;
 	}
@@ -342,9 +349,12 @@ public class OptionsTag extends AbstractHtmlElementTag {
 	 */
 	private class OptionsWriter extends OptionWriter {
 
+		@Nullable
 		private final String selectName;
 
-		public OptionsWriter(String selectName, Object optionSource, String valueProperty, String labelProperty) {
+		public OptionsWriter(@Nullable String selectName, Object optionSource,
+				@Nullable String valueProperty, @Nullable String labelProperty) {
+
 			super(optionSource, getBindStatus(), valueProperty, labelProperty, isHtmlEscape());
 			this.selectName = selectName;
 		}
@@ -364,7 +374,6 @@ public class OptionsTag extends AbstractHtmlElementTag {
 		protected String processOptionValue(String value) {
 			return processFieldValue(this.selectName, value, "option");
 		}
-
 	}
 
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/RadioButtonTag.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/SelectTag.java

@@ -20,6 +20,7 @@ import java.util.Collection;
 import java.util.Map;
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.servlet.support.BindStatus;
@@ -255,39 +256,45 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 
 
 	/**
-	 * The {@link Collection}, {@link Map} or array of objects used to generate the inner
-	 * '{@code option}' tags.
+	 * The {@link Collection}, {@link Map} or array of objects used to generate
+	 * the inner '{@code option}' tags.
 	 */
+	@Nullable
 	private Object items;
 
 	/**
 	 * The name of the property mapped to the '{@code value}' attribute
 	 * of the '{@code option}' tag.
 	 */
+	@Nullable
 	private String itemValue;
 
 	/**
 	 * The name of the property mapped to the inner text of the
 	 * '{@code option}' tag.
 	 */
+	@Nullable
 	private String itemLabel;
 
 	/**
 	 * The value of the HTML '{@code size}' attribute rendered
 	 * on the final '{@code select}' element.
 	 */
+	@Nullable
 	private String size;
 
 	/**
 	 * Indicates whether or not the '{@code select}' tag allows
 	 * multiple-selections.
 	 */
+	@Nullable
 	private Object multiple;
 
 	/**
 	 * The {@link TagWriter} instance that the output is being written.
 	 * <p>Only used in conjunction with nested {@link OptionTag OptionTags}.
 	 */
+	@Nullable
 	private TagWriter tagWriter;
 
 
@@ -299,7 +306,7 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 	 * <p>Typically a runtime expression.
 	 * @param items the items that comprise the options of this selection
 	 */
-	public void setItems(Object items) {
+	public void setItems(@Nullable Object items) {
 		this.items = (items != null ? items : EMPTY);
 	}
 
@@ -307,6 +314,7 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 	 * Get the value of the '{@code items}' attribute.
 	 * <p>May be a runtime expression.
 	 */
+	@Nullable
 	protected Object getItems() {
 		return this.items;
 	}
@@ -326,6 +334,7 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 	 * Get the value of the '{@code itemValue}' attribute.
 	 * <p>May be a runtime expression.
 	 */
+	@Nullable
 	protected String getItemValue() {
 		return this.itemValue;
 	}
@@ -343,6 +352,7 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 	 * Get the value of the '{@code itemLabel}' attribute.
 	 * <p>May be a runtime expression.
 	 */
+	@Nullable
 	protected String getItemLabel() {
 		return this.itemLabel;
 	}
@@ -358,6 +368,7 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code size}' attribute.
 	 */
+	@Nullable
 	protected String getSize() {
 		return this.size;
 	}
@@ -374,6 +385,7 @@ public class SelectTag extends AbstractHtmlInputElementTag {
 	 * Get the value of the HTML '{@code multiple}' attribute rendered
 	 * on the final '{@code select}' element.
 	 */
+	@Nullable
 	protected Object getMultiple() {
 		return this.multiple;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/SelectedValueComparator.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.servlet.support.BindStatus;
@@ -59,11 +60,7 @@ abstract class SelectedValueComparator {
 	 * the supplied {@link BindStatus}. Equality in this case differs from standard Java equality and
 	 * is described in more detail <a href="#equality-contract">here</a>.
 	 */
-	public static boolean isSelected(BindStatus bindStatus, Object candidateValue) {
-		if (bindStatus == null) {
-			return (candidateValue == null);
-		}
-
+	public static boolean isSelected(BindStatus bindStatus, @Nullable Object candidateValue) {
 		// Check obvious equality matches with the candidate first,
 		// both with the rendered value and with the original value.
 		Object boundValue = bindStatus.getValue();
@@ -85,14 +82,16 @@ abstract class SelectedValueComparator {
 		// Non-null value but no obvious equality with the candidate value:
 		// go into more exhaustive comparisons.
 		boolean selected = false;
-		if (boundValue.getClass().isArray()) {
-			selected = collectionCompare(CollectionUtils.arrayToList(boundValue), candidateValue, bindStatus);
-		}
-		else if (boundValue instanceof Collection) {
-			selected = collectionCompare((Collection<?>) boundValue, candidateValue, bindStatus);
-		}
-		else if (boundValue instanceof Map) {
-			selected = mapCompare((Map<?, ?>) boundValue, candidateValue, bindStatus);
+		if (candidateValue != null) {
+			if (boundValue.getClass().isArray()) {
+				selected = collectionCompare(CollectionUtils.arrayToList(boundValue), candidateValue, bindStatus);
+			}
+			else if (boundValue instanceof Collection) {
+				selected = collectionCompare((Collection<?>) boundValue, candidateValue, bindStatus);
+			}
+			else if (boundValue instanceof Map) {
+				selected = mapCompare((Map<?, ?>) boundValue, candidateValue, bindStatus);
+			}
 		}
 		if (!selected) {
 			selected = exhaustiveCompare(boundValue, candidateValue, bindStatus.getEditor(), null);
@@ -100,8 +99,8 @@ abstract class SelectedValueComparator {
 		return selected;
 	}
 
-	private static boolean collectionCompare(Collection<?> boundCollection, Object candidateValue,
-			BindStatus bindStatus) {
+	private static boolean collectionCompare(
+			Collection<?> boundCollection, Object candidateValue, BindStatus bindStatus) {
 		try {
 			if (boundCollection.contains(candidateValue)) {
 				return true;
@@ -128,7 +127,7 @@ abstract class SelectedValueComparator {
 	private static boolean exhaustiveCollectionCompare(
 			Collection<?> collection, Object candidateValue, BindStatus bindStatus) {
 
-		Map<PropertyEditor, Object> convertedValueCache = new HashMap<>(1);
+		Map<PropertyEditor, Object> convertedValueCache = new HashMap<>();
 		PropertyEditor editor = null;
 		boolean candidateIsString = (candidateValue instanceof String);
 		if (!candidateIsString) {
@@ -145,8 +144,8 @@ abstract class SelectedValueComparator {
 		return false;
 	}
 
-	private static boolean exhaustiveCompare(Object boundValue, Object candidate,
-			PropertyEditor editor, Map<PropertyEditor, Object> convertedValueCache) {
+	private static boolean exhaustiveCompare(@Nullable Object boundValue, @Nullable Object candidate,
+			@Nullable PropertyEditor editor, @Nullable Map<PropertyEditor, Object> convertedValueCache) {
 
 		String candidateDisplayString = ValueFormatter.getDisplayString(candidate, editor, false);
 		if (boundValue != null && boundValue.getClass().isEnum()) {

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/TagWriter.java

@@ -195,7 +195,7 @@ public class TagWriter {
 	}
 
 	private TagStateEntry currentState() {
-		return this.tagState.peek();
+		return this.tagState.element();
 	}
 
 
@@ -232,8 +232,10 @@ public class TagWriter {
 	 */
 	private static final class SafeWriter {
 
+		@Nullable
 		private PageContext pageContext;
 
+		@Nullable
 		private Writer writer;
 
 		public SafeWriter(PageContext pageContext) {
@@ -255,7 +257,9 @@ public class TagWriter {
 		}
 
 		private Writer getWriterToUse() {
-			return (this.pageContext != null ? this.pageContext.getOut() : this.writer);
+			Writer writer = (this.pageContext != null ? this.pageContext.getOut() : this.writer);
+			Assert.state(writer != null, "No Writer available");
+			return writer;
 		}
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/TextareaTag.java

@@ -18,6 +18,8 @@ package org.springframework.web.servlet.tags.form;
 
 import javax.servlet.jsp.JspException;
 
+import org.springframework.lang.Nullable;
+
 /**
  * The {@code <textarea>} tag renders an HTML 'textarea'.
  *
@@ -225,13 +227,14 @@ public class TextareaTag extends AbstractHtmlInputElementTag {
 
 	public static final String ONSELECT_ATTRIBUTE = "onselect";
 
-	public static final String READONLY_ATTRIBUTE = "readonly";
-
 
+	@Nullable
 	private String rows;
 
+	@Nullable
 	private String cols;
 
+	@Nullable
 	private String onselect;
 
 
@@ -246,6 +249,7 @@ public class TextareaTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code rows}' attribute.
 	 */
+	@Nullable
 	protected String getRows() {
 		return this.rows;
 	}
@@ -261,6 +265,7 @@ public class TextareaTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code cols}' attribute.
 	 */
+	@Nullable
 	protected String getCols() {
 		return this.cols;
 	}
@@ -276,6 +281,7 @@ public class TextareaTag extends AbstractHtmlInputElementTag {
 	/**
 	 * Get the value of the '{@code onselect}' attribute.
 	 */
+	@Nullable
 	protected String getOnselect() {
 		return this.onselect;
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/ValueFormatter.java

 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ package org.springframework.web.servlet.tags.form;
 
 import java.beans.PropertyEditor;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.util.HtmlUtils;
 
@@ -43,7 +44,7 @@ abstract class ValueFormatter {
 	 * as required. This version is <strong>not</strong> {@link PropertyEditor}-aware.
 	 * @see #getDisplayString(Object, java.beans.PropertyEditor, boolean)
 	 */
-	public static String getDisplayString(Object value, boolean htmlEscape) {
+	public static String getDisplayString(@Nullable Object value, boolean htmlEscape) {
 		String displayValue = ObjectUtils.getDisplayString(value);
 		return (htmlEscape ? HtmlUtils.htmlEscape(displayValue) : displayValue);
 	}
@@ -55,7 +56,9 @@ abstract class ValueFormatter {
 	 * to obtain the display value.
 	 * @see #getDisplayString(Object, boolean)
 	 */
-	public static String getDisplayString(Object value, PropertyEditor propertyEditor, boolean htmlEscape) {
+	public static String getDisplayString(
+			@Nullable Object value, @Nullable PropertyEditor propertyEditor, boolean htmlEscape) {
+
 		if (propertyEditor != null && !(value instanceof String)) {
 			try {
 				propertyEditor.setValue(value);

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/package-info.java

 /**
- * Spring's form tag library for JSP 2.0+.
- * Supports JSP view implementations for Spring's web MVC framework.
+ * Spring's form tag library for JSP views in Spring's Web MVC framework.
  * For more details on each tag, see the list of tags below with links to
  * individual tag classes, or check the {@code spring-form.tld} file:
  *
@@ -22,4 +21,9 @@
  * <li>{@link org.springframework.web.servlet.tags.form.TextareaTag The textarea tag}
  * </ul>
  */
+@NonNullApi
+@NonNullFields
 package org.springframework.web.servlet.tags.form;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;