noting why I'm doing a null check.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@16422 71c3de6d-444a-0410-be80-ed276b4c234a

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

@@ -276,6 +276,8 @@ public abstract class Trigger<J extends Item> implements Describable<Trigger<?>>
 
             if (i instanceof TopLevelItem) {// ugly
                 TopLevelItemDescriptor tld = ((TopLevelItem) i).getDescriptor();
+                // tld shouldn't be really null in contract, but we often write test Describables that
+                // doesn't have a Descriptor.
                 if(tld!=null && !tld.isApplicable(t))    continue;
             }