code: public HttpRequest buildRequest(String requestMethod, GenericUrl url, HttpContent content)
        throws IOException {
      HttpRequest request = transport.buildRequest();
      if (initializer != null) {
        initializer.initialize(request);
      }
      request.setRequestMethod(requestMethod);
      if (url != null) {
        request.setUrl(url);
      }
      if (content != null) {
        request.setContent(content);
      }
      return request;
    }
docs: Builds a request for the given HTTP method, URL, and content.
  
  @param requestMethod HTTP request method
  @param url HTTP request URL or {@code null} for none
  @param content HTTP request content or {@code null} for none
  @return new HTTP request
  @since 1.12