docs: @Override
      public String getPortletHeadOutput(
              IPortletWindowId portletWindowId,
              HttpServletRequest request,
              HttpServletResponse response) {
          if (doesPortletNeedHeaderWorker(portletWindowId, request)) {
              final IPortletRenderExecutionWorker tracker =
                      getRenderedPortletHeaderWorker(portletWindowId, request, response);
              final long timeout = getPortletRenderTimeout(portletWindowId, request);
              try {
                  final String output = tracker.getOutput(timeout);
                  return output == null ? "" : output;
              } catch (Exception e) {
                  logger.error("failed to render header output for " + portletWindowId, e);
                  return "";
              }
          }
  
          logger.debug(portletWindowId + " does not produce output for header");
          return "";
      }