@Override
  protected void checkTransition(RegionStateNode regionNode, TransitionCode transitionCode,
    long seqId) throws UnexpectedStateException {
    if (transitionCode != TransitionCode.CLOSED) {
      throw new UnexpectedStateException("Received report unexpected " + transitionCode
        + " transition, " + regionNode.toShortString() + ", " + this + ", expected CLOSED.");
    }
  }
The remote procedure used to close a region.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/CloseRegionProcedure.java