I think I'm misunderstanding something. By my reading of the code, the syntax of the filter flag is:

    --filter=com.google.testing.Include=arg

It sounds like you are suggesting that the following two could mean different things:

    --filter=com.google.testing.Include
    --filter=com.google.testing.Include=

That seems a bit confusing. Can you give an example where these would mean something different?