static QueryParams queryParams(@Nullable String datacenter, @Nullable String filter) {
        final QueryParamsBuilder paramsBuilder = QueryParams.builder();
        if (datacenter != null) {
            paramsBuilder.add(DATACENTER_PARAM, datacenter);
        }
        if (filter != null) {
            paramsBuilder.add(FILTER_PARAM, filter);
        }
        return paramsBuilder.build();
    }
Encodes common Consul API parameters as {@code QueryParams}.
consul/src/main/java/com/linecorp/armeria/internal/consul/ConsulClientUtil.java