AttributeError: 'NoneType' object has no attribute 'replace'

[rbnmurthy2000]

Trying to run the following command
python xlsx2reqif.py "Trial Quality ReqIF download.xlsx"

ERROR:

C:\Temp\pyreqif>python xlsx2reqif.py "Trial Quality ReqIF download.xlsx"
Traceback (most recent call last):
File "xlsx2reqif.py", line 96, in
pyreqif.create.addReqType("some_requirement_type_id", "requirement Type", "reqtype_for" + col.replace(" ", ""),
AttributeError: 'NoneType' object has no attribute 'replace'