writeJsonResponse(HttpServletResponse.SC_BAD_REQUEST, escapeJsonKeyValue(MESSAGE_FIELD, "Referer is invalid."));
            return;
        }

        if (!fessConfig.isApiSearchScroll()) {
            writeJsonResponse(HttpServletResponse.SC_BAD_REQUEST, escapeJsonKeyValue(MESSAGE_FIELD, "Scroll Search is not available."));
            return;
        }