/// <summary>
/// Initializes a new instance of the <see cref="SubscriptionState"/> class.
/// </summary>
/// <param name="state">State to copy.</param>
private SubscriptionState(SubscriptionState state)
{
if (state == null)
throw new ArgumentNullException("state");
Expires = state.Expires;
Reason = state.Reason;
RetryAfter = state.RetryAfter;
State = state.State;
}