[FIXED HUDSON-2527] Fixed NPE and instead deal with this gracefully.

Improved doc to call out for this error-prone definition of semantics.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@12850 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/Functions.java

@@ -866,6 +866,7 @@ public class Functions {
      */
     public static String getActionUrl(String itUrl,Action action) {
         String urlName = action.getUrlName();
+        if(urlName==null)   return null;    // to avoid NPE and fail to render the whole page
 
         if(SCHEME.matcher(urlName).matches())
             return urlName; // absolute URL