return null from invariant when optimized away

Summary: The original function doesn't return anything, so when we optimize it, it should stay true to that.

Reviewed By: @markw65

Differential Revision: D1403616
allow test files to have spaces

Summary: I'm fixing rex's tests, and his directory had  spaces in it

Reviewed By: @JoelMarcey

Differential Revision: D1399781