code: public void rollback() throws SystemException {
          Transaction transaction = currentTransaction();
          if (transaction == null) {
              throw new IllegalStateException("No active transaction");
          }
          transaction.rollback();     
      }
docs: Rolls back the current transaction, if one exists.
  
  @throws IllegalStateException If the calling thread is not associated with a transaction.
  @throws SystemException If the transaction service fails in an unexpected way.