code: public void resume( javax.transaction.Transaction transaction ) throws SystemException {
          if (transaction != null && txnMgr.getTransaction() == null) {
              try {
                  txnMgr.resume(transaction);
              } catch (InvalidTransactionException e) {
                  throw new RuntimeException(e);
              }
          }
      }
docs: Resumes a transaction that was previously suspended via the {@link org.modeshape.jcr.txn.Transactions#suspend()} call. If
  there is no such transaction or there is another active transaction, nothing happens.
  
  @param transaction a {@link javax.transaction.Transaction} instance which was suspended previously or {@code null}
  @throws javax.transaction.SystemException if the operation fails.
  @see javax.transaction.TransactionManager#resume(javax.transaction.Transaction)