private Uri GetDocumentUri(string key)
{
    return UriFactory.CreateDocumentUri(
        _options.DatabaseName,
        _options.CollectionName,
        key);
}

public async Task<byte[]> GetAsync(string key, CancellationToken token)
{
    var uri = this.GetDocumentUri(key);

    try
    {
        var result = await _client
            .ReadDocumentAsync<CosmosDbCacheItem>(uri, new RequestOptions() { });

        return result.Document.ToByteContent();
    }
    catch (DocumentClientException)
    {
        return null;
    }
}