Map<String, String[]> paramMap;

        paramMap = filter.parseQueryString("a=", "UTF-8");
        assertEquals(1, paramMap.size());
        assertEquals("", paramMap.get("a")[0]);

        paramMap = filter.parseQueryString("a", "UTF-8");
        assertEquals(1, paramMap.size());
        assertEquals("", paramMap.get("a")[0]);

        paramMap = filter.parseQueryString("=1", "UTF-8");
        assertEquals(1, paramMap.size());

        final String queryString = request.getQueryString();
        if (StringUtil.isNotBlank(queryString)) {
            return parseQueryString(queryString, enc);
        }
        return Collections.emptyMap();
    }

    /**
     * Parses a query string and extracts parameter name-value pairs.