docs: @SuppressWarnings("unchecked")
      protected Map<IPortletWindowId, Exception> getPortletErrorMap(HttpServletRequest request) {
          final HttpSession session = request.getSession();
          synchronized (WebUtils.getSessionMutex(session)) {
              Map<IPortletWindowId, Exception> portletFailureMap =
                      (Map<IPortletWindowId, Exception>)
                              session.getAttribute(SESSION_ATTRIBUTE__PORTLET_FAILURE_CAUSE_MAP);
              if (portletFailureMap == null) {
                  portletFailureMap = new ConcurrentHashMap<IPortletWindowId, Exception>();
                  session.setAttribute(
                          SESSION_ATTRIBUTE__PORTLET_FAILURE_CAUSE_MAP, portletFailureMap);
              }
              return portletFailureMap;
          }
      }