/// <summary>
 /// Add requests that we are waiting for.
 /// </summary>
 /// <param name="waitingForRequestIds">Requests that we are waiting for</param>
 /// <returns></returns>
 public RequestPostponedException AddWaitingForIds(params string[] waitingForRequestIds)
 {
     if (waitingForRequestIds == null)
     {
         return(this);
     }
     WaitingForRequestIds.AddRange(waitingForRequestIds.Where(ri => ri != null));
     return(this);
 }
 /// <summary>
 /// Add requests that we are waiting for.
 /// </summary>
 /// <param name="waitingForRequestIds">Requests that we are waiting for</param>
 /// <returns></returns>
 public RequestPostponedException AddWaitingForIds(IEnumerable <string> waitingForRequestIds)
 {
     if (waitingForRequestIds == null)
     {
         return(this);
     }
     WaitingForRequestIds.AddRange(waitingForRequestIds.Where(ri => ri != null));
     return(this);
 }