YARN-10651. CapacityScheduler crashed with NPE in AbstractYarnScheduler.updateNodeResource(). Contributed by Haibo Chen

(cherry picked from commit f348ab3f2f468751af329a1ffce4917cb000fcbf)
(cherry picked from commit be6e99963ded94adf6f447ff53f2ba66b99120ca)
(cherry picked from commit 6863a5bb8ace591de3374102920bba916dbebfda)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/AbstractYarnScheduler.java

@@ -834,6 +834,11 @@ public abstract class AbstractYarnScheduler
     try {
       writeLock.lock();
       SchedulerNode node = getSchedulerNode(nm.getNodeID());
+      if (node == null) {
+        LOG.info("Node: " + nm.getNodeID() + " has already been taken out of " +
+            "scheduling. Skip updating its resource");
+        return;
+      }
       Resource newResource = resourceOption.getResource();
       Resource oldResource = node.getTotalResource();
       if (!oldResource.equals(newResource)) {