AttributeError in resolvers.py in pip20.3.1

[shuklak13]

What did you want to do?

I attempted to run pip install -q -U seaborn scikit-learn model-card-toolkit on pip version 20.3.1.

Output

ERROR: Exception:
Traceback (most recent call last):
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_internal/cli/base_command.py", line 224, in _main
    status = self.run(options, args)
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_internal/cli/req_command.py", line 180, in wrapper
    return func(self, options, args)
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_internal/commands/install.py", line 321, in run
    reqs, check_supported_wheels=not options.target_dir
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_internal/resolution/resolvelib/resolver.py", line 122, in resolve
    requirements, max_rounds=try_to_avoid_resolution_too_deep,
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_vendor/resolvelib/resolvers.py", line 445, in resolve
    state = resolution.resolve(requirements, max_rounds=max_rounds)
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_vendor/resolvelib/resolvers.py", line 325, in resolve
    for item in self.state.criteria.items()
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_vendor/resolvelib/resolvers.py", line 326, in <listcomp>
    if not self._is_current_pin_satisfying(*item)
  File "/tmpfs/src/temp_venv/lib/python3.6/site-packages/pip/_vendor/resolvelib/resolvers.py", line 193, in _is_current_pin_satisfying
    for r in criterion.iter_requirement()
AttributeError: 'NoneType' object has no attribute 'iter_requirement'

Additional information

My pip freeze: https://gist.githubusercontent.com/shuklak13/0d206d1e69f259561ce83880f688b40a/raw/fbbf2451b3f9936c2d73edec35ab9e4973eead8a/pip%2520freeze

My pipdeptree: https://gist.githubusercontent.com/shuklak13/0d206d1e69f259561ce83880f688b40a/raw/fbbf2451b3f9936c2d73edec35ab9e4973eead8a/pipdeptree

[uranusjr]

Already tracked in #9180.