HDFS-13155. BlockPlacementPolicyDefault.chooseTargetInOrder Not Checking Return Value for NULL. Contributed by Zsolt Venczel.

(cherry picked from commit bccdfeee0aaef9cb98d09ee39909b63fdcbeeafc)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java

@@ -480,9 +480,13 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
                                  throws NotEnoughReplicasException {
     final int numOfResults = results.size();
     if (numOfResults == 0) {
-      writer = chooseLocalStorage(writer, excludedNodes, blocksize,
-          maxNodesPerRack, results, avoidStaleNodes, storageTypes, true)
-          .getDatanodeDescriptor();
+      DatanodeStorageInfo storageInfo = chooseLocalStorage(writer,
+          excludedNodes, blocksize, maxNodesPerRack, results, avoidStaleNodes,
+          storageTypes, true);
+
+      writer = (storageInfo != null) ? storageInfo.getDatanodeDescriptor()
+                                     : null;
+
       if (--numOfReplicas == 0) {
         return writer;
       }