For me it happened because source csv file was generated with python without opening file with option
newline="", so when I open it on for example Google Sheets, it looks like this:
Probably that empty rows are "NoneType".
UPD. Also, when I fixed empty rows, it still refused to upload file using Chrome on Windows. When I tried to do that using Firefox it was finally successful.
How are you uploading (I assume from the "Add Data" option from the launcher, or a similar method, and not from a UF)?
Does this happen with any file, and if not, what is in the file?