code: protected final O execute(HttpMethod method, String path, @Nullable String query, @Nullable String fragment,
                                I req, BiFunction<ClientRequestContext, Throwable, O> fallback) {
          return execute(null, method, path, query, fragment, req, fallback);
      }
docs: Executes the specified {@link Request} via {@link #delegate()}.
  
  @param method the method of the {@link Request}
  @param path the path part of the {@link Request} URI
  @param query the query part of the {@link Request} URI
  @param fragment the fragment part of the {@link Request} URI
  @param req the {@link Request}
  @param fallback the fallback response {@link BiFunction} to use when
  {@link Client#execute(ClientRequestContext, Request)} of {@link #delegate()} throws
  an exception instead of returning an error response