Read Organizer.SentBy throw exception

[idiotsky]

When Parameters.Get("SENT-BY") return null. when read Organizer.SentBy will throw exception. public virtual Uri SentBy { get => new Uri(this.Parameters.Get("SENT-BY")); } should be something like public virtual Uri SentBy { get { if(this.Parameters.Get("SENT-BY") != null) { new Uri(this.Parameters.Get("SENT-BY")); } return null. } }

[axunonb]

Appreciate a PR. Please double-check the new version merged with #595