public void validate(Supplier<String> etagSupplier) {

        String etag = etagSupplier.get();
        if (etag == null) {
            // Resource doesn't exist
            return;
        }

        validateIfMatch(etag);

        validateIfNoneMatch(etag);
    }
Http method, e.g. GET, PUT, POST and etc
storage/src/main/java/com/epam/aidial/core/storage/util/EtagHeader.java