Add method
Implementation
void Add(GroupMember member) {
EwsUtilities.ValidateParam(member, "member");
EwsUtilities.Assert(member.Key == null, "GroupMemberCollection.Add",
"member.Key is not null.");
EwsUtilities.Assert(!this.Contains(member), "GroupMemberCollection.Add",
"The member is already in the collection");
this.InternalAdd(member);
}