YARN-9968. Public Localizer is exiting in NodeManager due to NullPointerException. Contributed by Tarun Parimi

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/localizer/ResourceLocalizationService.java

@@ -995,8 +995,10 @@ public class ResourceLocalizationService extends CompositeService
                 getLocalResourcesTracker(LocalResourceVisibility.APPLICATION, user, applicationId);
               final String diagnostics = "Failed to download resource " +
                   assoc.getResource() + " " + e.getCause();
-              tracker.handle(new ResourceFailedLocalizationEvent(
-                  assoc.getResource().getRequest(), diagnostics));
+              if(tracker != null) {
+                tracker.handle(new ResourceFailedLocalizationEvent(
+                    assoc.getResource().getRequest(), diagnostics));
+              }
               publicRsrc.handle(new ResourceFailedLocalizationEvent(
                   assoc.getResource().getRequest(), diagnostics));
               LOG.error(diagnostics);