code: public Map<String, Object> populateJsonResponse(String responseBody) throws JoseException {
          if (responseBody == null || responseBody.isEmpty()) {
              return null;
          }
          return JsonUtil.parseJson(responseBody);
      }
docs: Populates a Map from the response body. This method expects the responseBody value to be in JSON format.
  
  @param responseBody
  @return {@code null} if the response body was {@code null} or empty. Otherwise returns a Map with all entries and values
  contained in the response body.
  @throws JoseException