code: public static void setBegunTxOnThread(BegunTx<?> begunTx) {
          if (begunTx == null) {
              String msg = "The argument[begunTx] must not be null.";
              throw new IllegalArgumentException(msg);
          }
          Stack<BegunTx<?>> stack = threadLocal.get();
          if (stack == null) {
              stack = new Stack<BegunTx<?>>();
              threadLocal.set(stack);
          }
          stack.add(begunTx);
      }
docs: Set prepared begun-tx on thread.
  @param begunTx The context of DB access. (NotNull)