Header parameters not removed when empty

[rage-shadowman]

When you leave your header parameter null, the placeholder becomes the value.

Ex:

@Header("X-Some-Header: {someHeader}")
@RequestLine("GET /?queryStuff={queryStuff}")
String someHeaderTest(@Param("someHeader") String someHeader, @Param("queryStuff") String queryStuff);

When passing in null values (api.someHeaderTest(null, null);) feign will remove the queryStuff parameter, but the header value for "X-Some-Header" ends up retaining the placeholder value of "{someHeader}".

If the null query parameters are removed, then the null header parameters should also be removed.