code: public String call(TDApiRequest apiRequest, Optional<String> apiKeyCache)
      {
          String content = submitRequest(apiRequest, apiKeyCache, stringContentHandler);
          if (logger.isTraceEnabled()) {
              logger.trace("response:\n{}", content);
          }
          return content;
      }
docs: Submit an API request and get the result as String value (e.g. json)
  
  @param apiRequest
  @param apiKeyCache
  @return