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

[Lamprolite]

Hello, I try to use litstudy, and I get csv data from Springer and Elsevier.
I define
docs1 = litstudy.load_springer_csv('search_results.csv')
docs2 = litstudy.load_scopus_csv('scopus_results(geoheritage).csv')
docs3 = litstudy.load_scopus_csv('scopus_results(geopark assessment or geoheritage assessment or geosite assessment or geodiversity assessment).csv')
docs4 = litstudy.load_scopus_csv('scopus_results(geoeducation).csv')
docs5 = litstudy.load_scopus_csv('scopus_results(geopark).csv')
docs6 = litstudy.load_scopus_csv('scopus_results(geopark and education).csv')

docs_csv = docs1 | docs2 | docs3| docs4| docs5 | docs6

And, each docs column edit as same as your exaple ieee1.csv

Then, run

and attribute error.

It has no problem else affiliation.
but I want to get informations of affiliations so, I try to this.
plz. hellp me