docs: @Override
      public Set<String> paramKeys() {
          Set<String> set = new HashSet<String>();
          set.addAll(C.<String>list(request.paramNames()));
          set.addAll(extraParams.keySet());
          set.addAll(bodyParams().keySet());
          set.remove("_method");
          set.remove("_body");
          return set;
      }