adding error check

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@7661 71c3de6d-444a-0410-be80-ed276b4c234a

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

@@ -54,6 +54,7 @@ public abstract class Actionable extends AbstractModelObject {
      * Short for <tt>getActions().add(a)</tt>
      */
     public void addAction(Action a) {
+        if(a==null) throw new IllegalArgumentException();
         getActions().add(a);
     }