Fix Javadoc in AcceptHeaderLocaleResolver

Closes gh-26793

spring-webmvc/src/main/java/org/springframework/web/servlet/i18n/AcceptHeaderLocaleResolver.java

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -72,7 +72,7 @@ public class AcceptHeaderLocaleResolver implements LocaleResolver {
 	/**
 	 * Configure a fixed default locale to fall back on if the request does not
 	 * have an "Accept-Language" header.
-	 * <p>By default this is not set in which case when there is "Accept-Language"
+	 * <p>By default this is not set in which case when there is no "Accept-Language"
 	 * header, the default locale for the server is used as defined in
 	 * {@link HttpServletRequest#getLocale()}.
 	 * @param defaultLocale the default locale to use