FIX 'NoneType' object has no attribute 'isalpha' (#2440)

passerbya

2025-03-20 5ee2f382b32c5c0beaa1c133b466a100c6fb7ebc

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BAC009S0764W0121 <|Speech|>
BAC009S0916W0489 <|Speech|>
asr_example_cn_en <|Speech|>
ID0012W0014 <|Speech|>