code: protected static String requireActiveTransaction() {
          return Optional.ofNullable(ACTIVE_TX_ID.get()).orElseThrow(() -> new RelationalProviderException(
                  RelationalProviderI18n.threadNotAssociatedWithTransaction,
                  Thread.currentThread().getName()));
      }
docs: Requires that an active transaction exists for the current calling thread.
  
  @return the ID of the active transaction, never {@code null}
  @throws RelationalProviderException if the current thread is not associated with a transaction.