defensive check for preventing issue #1537

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@8486 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/tasks/BuildTrigger.java

@@ -60,6 +60,8 @@ public class BuildTrigger extends Publisher implements DependecyDeclarer, Matrix
     }
 
     public BuildTrigger(String childProjects, Result threshold) {
+        if(childProjects==null)
+            throw new IllegalArgumentException();
         this.childProjects = childProjects;
         this.threshold = threshold;
     }