private ServerName getServerName(final MasterProcedureEnv env) {
    if (regionLocation == null) {
      regionLocation =
        env.getAssignmentManager().getRegionStates().getRegionServerOfRegion(regionsToMerge[0]);
      // May still be null here but return null and let caller deal.
      // Means we lost the in-memory-only location. We are in recovery
      // or so. The caller should be able to deal w/ a null ServerName.
      // Let them go to the Balancer to find one to use instead.
    }
    return regionLocation;
  }
The procedure could be restarted from a different machine. If the variable is null, we need to
retrieve it.
@param env MasterProcedureEnv
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/MergeTableRegionsProcedure.java