added another convenience method.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@5776 71c3de6d-444a-0410-be80-ed276b4c234a

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

@@ -515,6 +515,16 @@ public class Util {
         return s;
     }
 
+    /**
+     * Convert empty string to null, and trim whitespace.
+     *
+     * @since 1.154
+     */
+    public static String fixEmptyAndTrim(String s) {
+        if(s==null)    return null;
+        return s.trim();
+    }
+
     /**
      * Cuts all the leading path portion and get just the file name.
      */