Potential defect in data graph

[sa-bpelakh]

@uscholdm observed the following when trying to generate a data graph:

onto_tool graphic --data -e https://user:password@agraph.semanticarts.com/catalogs/ibb/repositories/2021-06-10_Test -o ibbTriples --exclude-pattern [Via]

I get these errors:

Processing predicates: |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX| 100.0% Complete
Traceback (most recent call last):
  File "c:\users\michael\appdata\local\programs\python\python37\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "c:\users\michael\appdata\local\programs\python\python37\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Users\Michael\AppData\Local\Programs\Python\Python37\Scripts\onto_tool.exe\__main__.py", line 7, in <module>
  File "c:\users\michael\appdata\local\programs\python\python37\lib\site-packages\onto_tool\onto_tool.py", line 1142, in run_tool
    main(sys.argv[1:] if len(sys.argv) > 1 else ['-h'])
  File "c:\users\michael\appdata\local\programs\python\python37\lib\site-packages\onto_tool\onto_tool.py", line 1129, in main
    show_shacl=args.show_shacl)
  File "c:\users\michael\appdata\local\programs\python\python37\lib\site-packages\onto_tool\onto_tool.py", line 321, in generate_graphic
    og.create_instance_graf()
  File "c:\users\michael\appdata\local\programs\python\python37\lib\site-packages\onto_tool\ontograph.py", line 549, in create_instance_graf
    max_common = max(occurs for class_data in data_dict.values() for occurs in class_data['links'].values())
ValueError: max() arg is an empty sequence

Need to look at how that sequence can end up empty - perhaps due to limit config?