fixed help text and reverting the text back to default.

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

@@ -619,6 +619,10 @@ public abstract class Run <JobT extends Job<JobT,RunT>,RunT extends Run<JobT,Run
         return displayName!=null;
     }
 
+    /**
+     * @param value
+     *      Set to null to revert back to the default "#NNN".
+     */
     public void setDisplayName(String value) throws IOException {
         checkPermission(UPDATE);
         this.displayName = value;
@@ -1843,7 +1847,7 @@ public abstract class Run <JobT extends Job<JobT,RunT>,RunT extends Run<JobT,Run
     }
 
     protected void submit(JSONObject json) throws IOException {
-        setDisplayName(json.getString("displayName"));
+        setDisplayName(Util.fixEmptyAndTrim(json.getString("displayName")));
         setDescription(json.getString("description"));
     }
 

core/src/main/resources/hudson/model/Run/configure.jelly

@@ -28,10 +28,10 @@ THE SOFTWARE.
     <l:main-panel>
       <div class="behavior-loading">${%LOADING}</div>
       <f:form method="post" action="configSubmit" name="config">
-        <f:entry title="${%DisplayName}" help="/help/project-config/displayName.html">
+        <f:entry title="${%DisplayName}" help="/help/run-config/displayName.html">
           <f:textbox name="displayName" value="${it.hasCustomDisplayName()?it.displayName:''}"/>
         </f:entry>
-        <f:entry title="${%Description}" help="/help/project-config/description.html">
+        <f:entry title="${%Description}" help="/help/run-config/description.html">
           <f:textarea name="description" value="${it.description}"/>
         </f:entry>
 

war/src/main/webapp/help/run-config/description.html

+<div>
+    This description is placed on the build top page so that visitors can
+    know what this build did. You can use any HTML tags here.
+</div>
\ No newline at end of file

war/src/main/webapp/help/run-config/displayName.html

+<div>
+    If set, this text is used instead of the default "#NNN" to point to this build. Leave this empty
+    to use the default.
+</div>
\ No newline at end of file