Passes including almost all dummy encodings

I don't think it's possible using regexp. You could use `String#force_encoding` to convert `"."` e.g. to `UTF-7`, but you can't create regexp with the same encoding, because it's a dummy one. You also can't convert string in `UTF-7` to something else (like I do with the other dummy encodings), because there's no converter for this encoding.

You could use `String#empty?` :)