KeyError: '<PAD>'

[Wud1]

Traceback (most recent call last):
File "C:/Users/Chenxinliang/Desktop/medical_record/code/pgn_tf2/train.py", line 49, in
train(params)
File "C:/Users/Chenxinliang/Desktop/medical_record/code/pgn_tf2/train.py", line 28, in train
dataset = batcher(vocab, params)
File "C:\Users\Chenxinliang\Desktop\medical_record\code\pgn_tf2\batcher.py", line 292, in batcher
params["mode"])
File "C:\Users\Chenxinliang\Desktop\medical_record\code\pgn_tf2\batcher.py", line 252, in batch_generator
"enc_input": vocab.word2id[Vocab.PAD_TOKEN],
KeyError: ''

运行您的PGN进行训练的时候这种报错，应该怎么解决呢?