docs: protected PortletApplicationContext createPortletApplicationContext(PortletContext sc) {
          Class<?> contextClass = determineContextClass(sc);
          if (!PortletApplicationContext.class.isAssignableFrom(contextClass)) {
              throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
                      "] is not of type [" + PortletApplicationContext.class.getName() + "]");
          }
          PortletApplicationContext wac =
                  (PortletApplicationContext) BeanUtils.instantiateClass(contextClass);
          return wac;
      }