Diagnosis of an NPE probably caused by a transient slave connection error.

java.lang.NullPointerException
	at hudson.tasks.CommandInterpreter.createScriptFile(CommandInterpreter.java:104)
	at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:66)
	at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:58)
	at com.cloudbees.hudson.plugins.modeling.impl.builder.BuilderImpl.perform(BuilderImpl.java:58)
	at hudson.plugins.m2extrasteps.M2ExtraStepsWrapper.executeBuildSteps(M2ExtraStepsWrapper.java:166)
	at hudson.plugins.m2extrasteps.M2ExtraStepsWrapper.access$200(M2ExtraStepsWrapper.java:43)
	at hudson.plugins.m2extrasteps.M2ExtraStepsWrapper$1.tearDown(M2ExtraStepsWrapper.java:137)
	at hudson.maven.MavenModuleSetBuild$RunnerImpl.doRun(MavenModuleSetBuild.java:817)
	at hudson.model.AbstractBuild$AbstractRunner.run(AbstractBuild.java:490)
	at hudson.model.Run.run(Run.java:1442)
	at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:477)
	at hudson.model.ResourceController.execute(ResourceController.java:88)
	at hudson.model.Executor.run(Executor.java:239)

core/src/main/java/hudson/model/AbstractBuild.java

@@ -263,7 +263,7 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
      * @return
      *      null, for example if the slave that this build run no longer exists.
      */
-    public Node getBuiltOn() {
+    public @CheckForNull Node getBuiltOn() {
         if (builtOn==null || builtOn.equals(""))
             return Jenkins.getInstance();
         else

core/src/main/java/hudson/model/AbstractCIBase.java

@@ -37,6 +37,7 @@ import java.io.IOException;
 import java.util.*;
 import java.util.concurrent.CopyOnWriteArraySet;
 import java.util.logging.Logger;
+import javax.annotation.CheckForNull;
 
 import jenkins.model.Configuration;
 
@@ -143,7 +144,7 @@ public abstract class AbstractCIBase extends Node implements ItemGroup<TopLevelI
         throw new IllegalStateException("Trying to remove unknown computer");
     }
 
-    /*package*/ Computer getComputer(Node n) {
+    /*package*/ @CheckForNull Computer getComputer(Node n) {
         Map<Node,Computer> computers = getComputerMap();
         return computers.get(n);
     }

core/src/main/java/hudson/model/Computer.java

@@ -25,14 +25,11 @@
 package hudson.model;
 
 import hudson.EnvVars;
-import hudson.FilePath;
-import hudson.Launcher;
 import hudson.Launcher.ProcStarter;
 import hudson.Util;
 import hudson.cli.declarative.CLIMethod;
 import hudson.cli.declarative.CLIResolver;
 import hudson.console.AnnotatedLargeText;
-import hudson.init.InitMilestone;
 import hudson.init.Initializer;
 import hudson.model.Descriptor.FormException;
 import hudson.model.labels.LabelAtom;
@@ -81,7 +78,6 @@ import javax.servlet.ServletException;
 import java.io.File;
 import java.io.FilenameFilter;
 import java.io.IOException;
-import java.io.OutputStream;
 import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.util.*;
@@ -100,6 +96,7 @@ import java.net.Inet4Address;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import javax.annotation.CheckForNull;
+import javax.annotation.Nullable;
 
 import static javax.servlet.http.HttpServletResponse.*;
 
@@ -281,7 +278,7 @@ public /*transient*/ abstract class Computer extends Actionable implements Acces
      * @return
      *      never null when {@link #isOffline()}==false.
      */
-    public abstract VirtualChannel getChannel();
+    public abstract @Nullable VirtualChannel getChannel();
 
     /**
      * Gets the default charset of this computer.

core/src/main/java/hudson/model/Node.java

@@ -57,6 +57,7 @@ import java.util.HashSet;
 import java.util.Set;
 import java.util.List;
 import java.util.logging.Logger;
+import javax.annotation.CheckForNull;
 
 import jenkins.model.Jenkins;
 import jenkins.util.io.OnMaster;
@@ -159,7 +160,7 @@ public abstract class Node extends AbstractModelObject implements Reconfigurable
      *      this method can return null if there's no {@link Computer} object for this node,
      *      such as when this node has no executors at all.
      */
-    public final Computer toComputer() {
+    public final @CheckForNull Computer toComputer() {
         AbstractCIBase ciBase = Jenkins.getInstance();
         return ciBase.getComputer(this);
     }
@@ -169,7 +170,7 @@ public abstract class Node extends AbstractModelObject implements Reconfigurable
      *
      * This is just a convenience method for {@link Computer#getChannel()} with null check. 
      */
-    public final VirtualChannel getChannel() {
+    public final @CheckForNull VirtualChannel getChannel() {
         Computer c = toComputer();
         return c==null ? null : c.getChannel();
     }
@@ -364,7 +365,7 @@ public abstract class Node extends AbstractModelObject implements Reconfigurable
     /**
      * Gets the {@link FilePath} on this node.
      */
-    public FilePath createPath(String absolutePath) {
+    public @CheckForNull FilePath createPath(String absolutePath) {
         VirtualChannel ch = getChannel();
         if(ch==null)    return null;    // offline
         return new FilePath(ch,absolutePath);

core/src/main/java/hudson/slaves/NodeList.java

@@ -39,6 +39,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CopyOnWriteArrayList;
+import javax.annotation.CheckForNull;
 
 /**
  * {@link CopyOnWriteArrayList} for {@link Node} that has special serialization semantics
@@ -67,7 +68,7 @@ public final class NodeList extends ArrayList<Node> {
         this(Arrays.asList(toCopyIn));
     }
     
-    public Node getNode(String nodeName) {
+    public @CheckForNull Node getNode(String nodeName) {
         return map.get(nodeName);
     }
 

core/src/main/java/hudson/tasks/CommandInterpreter.java

@@ -29,10 +29,12 @@ import hudson.Util;
 import hudson.EnvVars;
 import hudson.model.AbstractBuild;
 import hudson.model.BuildListener;
+import hudson.model.Node;
 import hudson.model.TaskListener;
 
 import java.io.IOException;
 import java.util.Map;
+import javax.annotation.Nonnull;
 
 /**
  * Common part between {@link Shell} and {@link BatchFile}.
@@ -60,6 +62,13 @@ public abstract class CommandInterpreter extends Builder {
 
     public boolean perform(AbstractBuild<?,?> build, Launcher launcher, TaskListener listener) throws InterruptedException {
         FilePath ws = build.getWorkspace();
+        if (ws == null) {
+            Node node = build.getBuiltOn();
+            if (node == null) {
+                throw new NullPointerException("no such build node: " + build.getBuiltOnStr());
+            }
+            throw new NullPointerException("no workspace from node " + node + " which is computer " + node.toComputer() + " and has channel " + node.getChannel());
+        }
         FilePath script=null;
         try {
             try {
@@ -100,7 +109,7 @@ public abstract class CommandInterpreter extends Builder {
     /**
      * Creates a script file in a temporary name in the specified directory.
      */
-    public FilePath createScriptFile(FilePath dir) throws IOException, InterruptedException {
+    public FilePath createScriptFile(@Nonnull FilePath dir) throws IOException, InterruptedException {
         return dir.createTextTempFile("hudson", getFileExtension(), getContents(), false);
     }
 

core/src/main/java/jenkins/model/Jenkins.java

@@ -1635,7 +1635,7 @@ public class Jenkins extends AbstractCIBase implements ModifiableTopLevelItemGro
     /**
      * Gets the slave node of the give name, hooked under this Hudson.
      */
-    public Node getNode(String name) {
+    public @CheckForNull Node getNode(String name) {
         return slaves.getNode(name);
     }