[FIXED HUDSON-3049] avoid NPE in DEFAULT ProcessTreeKiller

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@15369 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/util/ProcessTreeKiller.java

@@ -168,7 +168,8 @@ public abstract class ProcessTreeKiller {
      */
     private static final ProcessTreeKiller DEFAULT = new ProcessTreeKiller() {
         public void kill(Process proc, Map<String, String> modelEnvVars) {
-            proc.destroy();
+            if (proc!=null)
+                proc.destroy();
             // kill by model unsupported
         }
     };