public void DeleteAttachment(string key, Guid?etag)
{
var attachmentPosition = Mutator.Attachments.FindValue(key);
if (attachmentPosition == null)
{
return;
}
Mutator.DecrementAttachmentCount();
EnsureValidEtag(key, attachmentPosition.Value, etag);
Mutator.Attachments.Remove(key);
}