code: private static URL constructDefaultUrl() {
          String jenkinsUrl = Jenkins.getInstance().getRootUrl();
          validateConfig(isNotEmpty(jenkinsUrl), Messages.global_config_url_is_empty());
          try {
              return new URL(jenkinsUrl + GitHubWebHook.get().getUrlName() + '/');
          } catch (MalformedURLException e) {
              throw new GHPluginConfigException(Messages.global_config_hook_url_is_malformed(e.getMessage()));
          }
      }
docs: Used by default in {@link #getHookUrl()}
  
  @return url to be used in GH hooks configuration as main endpoint
  @throws GHPluginConfigException if jenkins root url empty of malformed