Fixing a Type Warning as per #1100

[evank28]

Fixing a Type Warning that resolves #1100 for PyCharm IDE users.

[skewty]

should it be Optional[Type[ObjectType]]? None seems to be an acceptable value.

[erikwrede]

We should fix all type hints and switch to this:
https://github.com/tox-dev/sphinx-autodoc-typehints

@skewty is right, Query should be optional. See types/schema.py:107 and graphql-core/type/schema.py:95. Closing this, as single-line type hint corrections don't solve the overall problem. PRs should be at least on a per-file basis to ensure we are not skimming through every file twice.