YARN-4510. Fix SLS startup failure caused by NPE. (Bibin A Chundatt via wangda)

(cherry picked from commit 6eefae1b33)

hadoop-tools/hadoop-sls/src/main/java/org/apache/hadoop/yarn/sls/scheduler/RMNodeWrapper.java

@@ -172,10 +172,11 @@ public class RMNodeWrapper implements RMNode {
     // TODO Auto-generated method stub
   }
 
+  @SuppressWarnings("unchecked")
   @Override
   public List<Container> pullNewlyIncreasedContainers() {
     // TODO Auto-generated method stub
-    return null;
+    return Collections.EMPTY_LIST;
   }
 
   @Override

hadoop-tools/hadoop-sls/src/main/java/org/apache/hadoop/yarn/sls/scheduler/ResourceSchedulerWrapper.java

@@ -819,6 +819,14 @@ final public class ResourceSchedulerWrapper
     ((AbstractYarnScheduler<SchedulerApplicationAttempt, SchedulerNode>)
         scheduler).init(conf);
     super.serviceInit(conf);
+    initScheduler(conf);
+  }
+
+  private synchronized void initScheduler(Configuration configuration) throws
+  IOException {
+    this.applications =
+        new ConcurrentHashMap<ApplicationId,
+        SchedulerApplication<SchedulerApplicationAttempt>>();
   }
 
   @SuppressWarnings("unchecked")

hadoop-yarn-project/CHANGES.txt

@@ -1260,6 +1260,8 @@ Release 2.7.3 - UNRELEASED
 
     YARN-4315. NaN in Queue percentage for cluster apps page. (Bibin A Chundatt via wangda)
 
+    YARN-4510. Fix SLS startup failure caused by NPE. (Bibin A Chundatt via wangda)
+
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES