code: public String queryParamOrDefault(String queryParam, String defaultValue) {
          String value = queryParams(queryParam);
          return value != null ? value : defaultValue;
      }
docs: Gets the query param, or returns default value
  
  @param queryParam   the query parameter
  @param defaultValue the default value
  @return the value of the provided queryParam, or default if value is null
  Example: query parameter 'id' from the following request URI: /hello?id=foo