**详细解决方法见链接：https://stackoverflow.com/questions/39808336/tensorflow-bidirectional-dynamic-rnn-none-values-error **
主要原因：tf.nn.bidirectional_dynamic_rnn（）中的参数sequence_length必须设置
tf.nn.bidirectional_dynamic_rnn（）函数详情链接：https://tensorflow.google.cn/api_docs/python/tf/nn/bidirectional_dynamic_rnn