pytype hook fails when only test files are updated.

[abadger]

I have a commit that only updates unit_test files. The pytype hook fails with a usage error:

pytype.......................................................................Failed
- hook id: pytype
- exit code: 2

usage: pytype [options] input [input ...]
pytype: error: Need an input.

I think that pre-commit ci must be invoking pytype because there are .py files in the commit but something is also removing the files from the invocation because they are in a tests/** subdirectory. Maybe the wrapper needs to be slightly heavier weight so that it can check whether there are any files before running pytype.