YARN-3425. NPE from RMNodeLabelsManager.serviceStop when NodeLabelsManager.serviceInit failed. (Bibin A Chundatt via wangda)

(cherry picked from commit 492239424a3ace9868b6154f44a0f18fa5318235)

hadoop-yarn-project/CHANGES.txt

@@ -81,6 +81,9 @@ Release 2.8.0 - UNRELEASED
 
     YARN-3412. RM tests should use MockRM where possible. (kasha)
 
+    YARN-3425. NPE from RMNodeLabelsManager.serviceStop when 
+    NodeLabelsManager.serviceInit failed. (Bibin A Chundatt via wangda)
+
 Release 2.7.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/nodelabels/CommonNodeLabelsManager.java

@@ -258,7 +258,9 @@ public class CommonNodeLabelsManager extends AbstractService {
   // for UT purpose
   protected void stopDispatcher() {
     AsyncDispatcher asyncDispatcher = (AsyncDispatcher) dispatcher;
-    asyncDispatcher.stop();
+    if (null != asyncDispatcher) {
+      asyncDispatcher.stop();
+    }
   }
   
   @Override