public void addTransaction(Transaction txn) throws SystemException {
    if (txn == null) {
      String exception =
          "GlobalTransaction::addTransaction::Cannot add a null Transaction";
      LogWriter writer = TransactionUtils.getLogWriter();
      if (VERBOSE) {
        writer.fine(exception);
      }
      throw new SystemException(exception);
    }
    transactions.add(txn);
  }
Add a transaction to the list of transactions participating in this global Transaction The list
of transactions is being maintained so that we can remove the local transaction to global
transaction entries from the map being maintained by the Transaction Manager

@param txn Transaction instance which is participating in this Global Transaction
geode-core/src/main/java/org/apache/geode/internal/jta/GlobalTransaction.java