public void applyConfig(ClientBwListDTO configDTO) {
        requireNonNull(configDTO, "Client filtering config must not be null");
        requireNonNull(configDTO.mode, "Config mode must not be null");
        requireNonNull(configDTO.entries, "Config entries must not be null");

        ClientSelector selector;
        switch (configDTO.mode) {
            case DISABLED:
                selector = ClientSelectors.any();
                break;
            case WHITELIST:
                selector = createSelector(configDTO.entries);
                break;
            case BLACKLIST:
                selector = ClientSelectors.inverse(createSelector(configDTO.entries));
                break;
            default:
                throw new IllegalArgumentException("Unknown client B/W list mode: " + configDTO.mode);
        }

        clientEngine.applySelector(selector);
    }
@Test
    public void testApplyConfig_nullMode_throws() {
        assertThrows(NullPointerException.class, () -> handler.applyConfig(createConfig(null)));
    }