@Override
  protected boolean abort(MasterProcedureEnv env) {
    // Abort means rollback. We can't rollback all steps. HBASE-18018 added abort to all
    // Procedures. Here is a Procedure that has a PONR and cannot be aborted once it enters this
    // range of steps; what do we do for these should an operator want to cancel them? HBASE-20022.
    return isRollbackSupported(getCurrentState()) && super.abort(env);
  }
Returns The merged region. Maybe be null if called to early or we failed.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/MergeTableRegionsProcedure.java