问题：AssertionError: CRF has not connected to any layer.

在运行bilstm_crf模型时，遇到CRF has not connected to any layer.的问题，想问问是为什么？怎么解决？具体报错内容如下： AssertionError: in user code:

File "E:\自然语言处理\KBQA\venv\lib\site-packages\keras\src\engine\training.py", line 1401, in train_function  *
    return step_function(self, iterator)
File "E:\自然语言处理\KBQA\knowledge_extraction\bilstm_crf\crf_layer.py", line 438, in loss  *
    assert self._inbound_nodes, 'CRF has not connected to any layer.'

AssertionError: CRF has not connected to any layer.

wangle1218 / KBQA-for-Diagnosis

问题：AssertionError: CRF has not connected to any layer. #43