Error when using `--flatten`

[MahShaaban]

Hi,
pathme kegg bel runs fine

2021-04-10 01:41:29,852 - INFO - pathme.cli - Initiating HGNC Manager
2021-04-10 01:41:29,939 - INFO - pathme.cli - Initiating ChEBI Manager
Exporting KEGG to BEL: 100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 343/343 [00:00<00:00, 116282.43it/s]
2021-04-10 01:41:29,963 - INFO - pathme.cli - KEGG exported in 0.11 seconds

but when I use the flag -f, I get an error

2021-04-10 01:41:37,070 - INFO - pathme.cli - Initiating HGNC Manager
2021-04-10 01:41:37,155 - INFO - pathme.cli - Initiating ChEBI Manager
2021-04-10 01:41:37,166 - INFO - pathme.cli - Flattening mode activated
Exporting KEGG to BEL:   0%|                                                                                                                                | 0/343 [00:00<?, ?it/s]
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.6/site-packages/pathme/__main__.py", line 8, in <module>
    main()
  File "/usr/local/lib/python3.6/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/pathme/cli.py", line 101, in bel
    export_folder=export_folder,
  File "/usr/local/lib/python3.6/site-packages/pathme/kegg/convert_to_bel.py", line 705, in kegg_to_pickles
    flatten=True if flatten else False,
  File "/usr/local/lib/python3.6/site-packages/pathme/kegg/convert_to_bel.py", line 80, in kegg_to_bel
    add_edges(graph, relations_list, nodes)
  File "/usr/local/lib/python3.6/site-packages/pathme/kegg/convert_to_bel.py", line 441, in add_edges
    add_simple_edge(graph, u, v, relation)
  File "/usr/local/lib/python3.6/site-packages/pathme/kegg/convert_to_bel.py", line 557, in add_simple_edge
    add_simple_edge(graph, u, v, relation)
  File "/usr/local/lib/python3.6/site-packages/pathme/kegg/convert_to_bel.py", line 646, in add_simple_edge
    raise ValueError(f'Unexpected relation type {relation_type} between {u} and {v}')
ValueError: Unexpected relation type indirect between p(HGNC:IL1R1) and p(HGNC:TRAF6)

I am using Python 3.6.5 inside a docker container Debian GNU/Linux 9 (stretch) which I built from this docker file

Thanks