poetry: EmptyKeyError when running poetry shell

• [x ] I am on the latest Poetry version.
• [ x] I have searched the issues of this repo and believe that this is not a duplicate.
• [x ] If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: MacOS Catalina 10.15.6
• Poetry version: 1.1.0b2
• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/jane-meichen-chen/2e220d50f311d266d0d02563f0fa03ce

Issue

When trying to run poetry shell, I get an EmptyKeyError:

% poetry shell

  EmptyKeyError

  Empty key at line 12 col 0

  at ~/.poetry/lib/poetry/_vendor/py3.7/tomlkit/parser.py:371 in _parse_key_value
       367│ 
       368│         # Key
       369│         key = self._parse_key()
       370│         if not key.key.strip():
    →  371│             raise self.parse_error(EmptyKeyError)
       372│ 
       373│         self.mark()
       374│ 
       375│         found_equals = self._current == "="

Please help. I don’t seem to find any similar issue on the internet, and believe this is not a duplication of an existing question.