@Override
    public String convert(ILoggingEvent event) {

        List<KeyValuePair> kvpList = event.getKeyValuePairs();
        if (kvpList == null || kvpList.isEmpty()) {
            return CoreConstants.EMPTY_STRING;
        }

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < kvpList.size(); i++) {
            KeyValuePair kvp = kvpList.get(i);
            if (i != 0)
                sb.append(' ');
            sb.append(String.valueOf(kvp.key));
            sb.append('=');
            Character quoteChar = valueQuoteSpec.asChar();
            if (quoteChar != null)
                sb.append(quoteChar);
            sb.append(String.valueOf(kvp.value));
            if (quoteChar != null)
                sb.append(quoteChar);
        }

        return sb.toString();
    }
@Test
    public void testWithNullKVPList() {
        // event.getKeyValuePairs().add(new KeyValuePair("k", "v"));
        String result = converter.convert(event);
        assertEquals("", result);
    }