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

[xraise17]

Hey I have been trying to run the your script by typing
python3 convert.py --input Apple_Summer0.obj --output Apple_Summer0.ply

and I am getting the following error:
Traceback (most recent call last):
File "file-converter-.obj-to-.ply/convert.py", line 122, in
args.func(args)
File "file-converter-.obj-to-.ply/convert.py", line 98, in main
result = mt.convert(args.input, output, up_conversion)
File "file-converter-.obj-to-.ply/d3/model/tools.py", line 98, in convert
return str(exporter)
File "file-converter-.obj-to-.ply/d3/model/formats/ply.py", line 489, in str
+ str(self.model.get_material_index(face.material))
File "file-converter-.obj-to-.ply/d3/model/basemodel.py", line 250, in get_material_index
return [i for (i,m) in enumerate(self.materials) if m.name == material.name][0]
File "file-converter-.obj-to-.ply/d3/model/basemodel.py", line 250, in
return [i for (i,m) in enumerate(self.materials) if m.name == material.name][0]
AttributeError: 'NoneType' object has no attribute 'name'

I am trying to debug the above error, I am thinking if I need to give more arguments?
I would appreciate any help,

Thanks in advance,
Christos P.