code: protected Operation httpOp(String method, HttpUrl url) {
          return new Operation(httpClient).method(method).httpUrl(url);
      }
docs: Starts an HTTP {@link Operation} with the given method and {@link HttpUrl}.
  
  @param method The uppercased HTTP method to use.
  @param url    An {@link HttpUrl} target.
  @return An {@link Operation} builder.