some Describables written for tests may return null.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@16421 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/triggers/Trigger.java

@@ -276,7 +276,7 @@ public abstract class Trigger<J extends Item> implements Describable<Trigger<?>>
 
             if (i instanceof TopLevelItem) {// ugly
                 TopLevelItemDescriptor tld = ((TopLevelItem) i).getDescriptor();
-                if(!tld.isApplicable(t))    continue;
+                if(tld!=null && !tld.isApplicable(t))    continue;
             }
 
             r.add(t);