public ExternalAnnotationsCache(DateTime lastWriteTimeUtc, [NotNull] ExternalAnnotationsMap externalAnnotations)
        {
            Guard.NotNull(externalAnnotations, nameof(externalAnnotations));

            LastWriteTimeUtc    = lastWriteTimeUtc;
            ExternalAnnotations = externalAnnotations;
        }
 public ExternalAnnotationsCache()
 {
     ExternalAnnotations = new ExternalAnnotationsMap();
 }