HBASE-28109 NPE for the region state: Failed to become active master (HMaster) (apache#5432)

The RegionState for meta region could be null for a fresh new cluster, we should also wait a bit to let it finish the initialization.

Signed-off-by: Duo Zhang <zhangduo@apache.org>

Author: hanke580

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

@@ -1412,7 +1412,7 @@ private boolean isRegionOnline(RegionInfo ri) {
     RetryCounter rc = null;
     while (!isStopped()) {
       RegionState rs = this.assignmentManager.getRegionStates().getRegionState(ri);
-      if (rs.isOpened()) {
+      if (rs != null && rs.isOpened()) {
         if (this.getServerManager().isServerOnline(rs.getServerName())) {
           return true;
         }