Summary:
We had a brief moment without Flow coverage, where this must have snuck
in. Not sure if there's a better type for `node` given the current
structure, but the rest should be obvious.
Pull Request resolved: https://github.com/facebook/flipper/pull/502
Test Plan: flow
Reviewed By: jknoxville
Differential Revision: D16533248
Pulled By: passy
fbshipit-source-id: 51e493208050e4af531e161fb49eda77fdf2494e
2dd580f24a