bifacial.pvfactors_timeseries() TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

Question

I am trying to run the function: bifacial.pvfactors_timeseries(), and get the error:

TypeError: unsupported operand type(s) for +=: \'NoneType\' and \'str\'.

I am