AttributeError from ontodoc

[lovfall]

I am trying to run ontodoc on an emmo compliant ontology, but get the following error:
Traceback (most recent call last):
File "/home/emmo/.local/bin/ontodoc", line 141, in
docpp = main()
File "/home/emmo/.local/bin/ontodoc", line 127, in main
docpp.process()
File "/home/emmo/.local/lib/python3.8/site-packages/emmo/ontodoc.py", line 813, in process
self.process_alls()
File "/home/emmo/.local/lib/python3.8/site-packages/emmo/ontodoc.py", line 741, in process_alls
self.lines[i: i] = self.ontodoc.itemsdoc(
File "/home/emmo/.local/lib/python3.8/site-packages/emmo/ontodoc.py", line 341, in itemsdoc
doc.append(self.itemdoc(item, header_level))
File "/home/emmo/.local/lib/python3.8/site-packages/emmo/ontodoc.py", line 241, in itemdoc
'', level=header_level, label=label, lowerlabel=label.lower()))
AttributeError: 'NoneType' object has no attribute 'lower'