protected TXRegionStub getTXRegionStub(InternalRegion region) {
    TXRegionStub stub = regionStubs.get(region);
    if (stub == null) {
      /*
       * validate whether this region is legit or not
       */
      validateRegionCanJoinTransaction(region);
      stub = generateRegionStub(region);
      regionStubs.put(region, stub);
    }
    return stub;
  }
Get or create a TXRegionStub for the given region. For regions that are new to the tx, we
validate their eligibility.

@param region The region to involve in the tx.
@return existing or new stub for region
geode-core/src/main/java/org/apache/geode/internal/cache/TXStateStub.java