@Documented
@Target(value=PARAMETER)
@Retention(value=RUNTIME)
public @interface Tag
@GET("/")
Call<ResponseBody> foo(@Tag String tag);
Tag arguments may be null which will omit them from the request. Passing a parameterized
type such as List<String> will use the raw type (i.e., List.class) as the key.
Duplicate tag types are not allowed.