您好,如图所示,训练前几个Batch有metric-f1值,之后变nan,产生这样的结果正常吗? <img width="769" alt="WeChatd771b6c880a207e21cb5b7f4c49d8f52" src="https://user-images.githubusercontent.com/25698117/78850334-8a513300-7a49-11ea-8e63-fa5351ce0010.png">