HBASE-10182 Potential null object deference in AssignmentManager#handleRegion()

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1551762 13f79535-47bb-0310-9956-ffa450edef68

hbase-server/src/main/java/org/apache/hadoop/hbase/master/AssignmentManager.java

@@ -924,10 +924,12 @@ public class AssignmentManager extends ZooKeeperListener {
               + " from " + sn + " but the region isn't PENDING_OPEN/OPENING here: "
               + regionStates.getRegionState(encodedName));
 
+            if (regionState != null) {
               // Close it without updating the internal region states,
               // so as not to create double assignments in unlucky scenarios
               // mentioned in OpenRegionHandler#process
               unassign(regionState.getRegion(), null, -1, null, false, sn);
+            }
             return;
           }
           // Handle OPENED by removing from transition and deleted zk node