needs to convert "" to null.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@5868 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/Util.java

@@ -522,7 +522,7 @@ public class Util {
      */
     public static String fixEmptyAndTrim(String s) {
         if(s==null)    return null;
-        return s.trim();
+        return fixEmpty(s.trim());
     }
 
     /**