Power Query condition column turn out error, cannot convert null to type logical

[Cheryl88]

I've imported a folder into a Power Query Table. All seems to appear ok until I remove empty in one column, I have no idea which step going wrong, please help, thx

[Poohkrd · Accepted solution]

Hi! Can you show Custom Function, which transforms each file in the folder before you combine them?

[Cheryl88]

I checked every file in this foler and found the reason, one of file's format is different from others, thx a lot