code: @Override
      public void validate(ValidationHelper helper, Context context, String key, Server t) {
          String url = t.getUrl();
  
          if (url != null) {
              Set<String> variables = validateURL(helper, context, url);
              //url can be relative - so shouldn't check for URL format here
              validateServerVariables(helper, context, variables, t);
          } else {
              ValidatorUtils.validateRequiredField(url, context, "url").ifPresent(helper::addValidationEvent);
  
          }
  
      }
docs: {@inheritDoc}