diff --git a/core/src/main/java/hudson/util/ProcessTreeKiller.java b/core/src/main/java/hudson/util/ProcessTreeKiller.java
index 814d594b5a6513adf065c77232ab37c2a65b9835..4313186773072ccb8ad7c937f02b9ce0c8453595 100644
--- a/core/src/main/java/hudson/util/ProcessTreeKiller.java
+++ b/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
         }
     };