Keras回调Tensorboard多输出错误

from keras.callbacks import Callback
from keras import backend as K
from tensorflow.summary import FileWriter

class CustomTensorboardCallback(Callback):
    def __init__(self, log_dir):
        super(CustomTensorboardCallback, self).__init__()
        self.log_dir = log_dir
        self.writer = FileWriter(log_dir)

    def on_epoch_end(self, epoch, logs=None):
        logs = logs or {}
        # 获取多个输出的数据
        output1 = self.model.get_layer('output1').output
        output2 = self.model.get_layer('output2').output
        # 合并多个输出的数据为一个张量
        merged_output = K.concatenate([output1, output2], axis=1)
        # 将合并后的张量传递给Tensorboard回调函数进行保存
        with self.writer.as_default():
            K.summary.histogram('merged_output', merged_output, step=epoch)
            for name, value in logs.items():
                K.summary.scalar(name, value, step=epoch)
            self.writer.flush()

# 创建自定义的Tensorboard回调函数对象
tensorboard_callback = CustomTensorboardCallback(log_dir='logs')

# 在模型训练时将自定义的Tensorboard回调函数传递给fit方法
model.fit(x_train, y_train, callbacks=[tensorboard_callback])