public bool Equals(SubscribedToNewsletter other)
 {
     if (ReferenceEquals(null, other))
     {
         return(false);
     }
     if (ReferenceEquals(this, other))
     {
         return(true);
     }
     return(Equals(other.NewsletterName, NewsletterName));
 }
 private void Apply(SubscribedToNewsletter evt)
 {
     _subscribedNewsletters.Add(evt.NewsletterName);
 }