sess.run中的TypeError，因为fetch参数的类型无效

Question

我的会话运行如下。

while batch_number < args.epoch_size:
    start_time = time.time()
    feed_dict = {
        learning_rate_placeholder: lr,
        phase_train_placeholder  : True,
        batch_size_placeholder   : args.batch_size}
    if (batch_number % 100 == 0):

        err, _, step, reg_loss, summary_str = sess.run(
            [loss, train_op, global_step, regularization_losses, summary_op], feed_dict=feed_dict)
        summary_writer.add_summary(summary_str, global_step=step)
    else:
        err, _, step, reg_loss = sess.run([loss, train_op, global_step, regularization_losses], feed_dict=feed_dict)
    duration = time.time() - start_time

出现以下错误，

  

TypeError：获取参数None的类型无效

错误在执行sess.run的行中发生。我可以知道为什么吗？有什么解决办法吗？