getting `clippy::match_single_binding` when creating empty service

sometimes we want to create a empty service for prototyping or some other reason, right now the codegen always generate a match statement which will give us a `clippy::match_single_binding` when there's no path to match which can be a little annoying
I recommend to either change the codegen to not use match when there's no variant, or just add `#[allow(clippy::match_single_binding)]` to the match just to be safe.
I can send a PR for each solution but I'm not sure which is better...
just adding allow can be simpler because at the end of the day this is a code generated with codegen...