HBASE-28226 Add logic to check for RegionStateNode null pointer in Fl…

…ushRegionProcedure (#5548)

Co-authored-by: lvhaiping.lhp <lvhaiping.lhp@alibaba-inc.com>
Signed-off-by: Duo Zhang <zhangduo@apache.org>
(cherry picked from commit 8631714)

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

@@ -88,6 +88,11 @@ protected Procedure<MasterProcedureEnv>[] execute(MasterProcedureEnv env)
 
     RegionStates regionStates = env.getAssignmentManager().getRegionStates();
     RegionStateNode regionNode = regionStates.getRegionStateNode(region);
+    if (regionNode == null) {
+      LOG.debug("Region {} is not in region states, it is very likely that it has been cleared by"
+        + " other procedures such as merge or split, so skip {}. See HBASE-28226", region, this);
+      return null;
+    }
     regionNode.lock();
     try {
       if (!regionNode.isInState(State.OPEN) || regionNode.isInTransition()) {