/// <summary>
 /// Unsubscribes from a push request.
 /// </summary>
 /// <param name="pushRequestSubscriptionManager">Push request subscription manager</param>
 /// <param name="user">User.</param>
 /// <param name="pushRequestName">Name of the push request.</param>
 /// <param name="entityIdentifier">entity identifier</param>
 public static void Unsubscribe(this IPushRequestSubscriptionManager pushRequestSubscriptionManager, UserIdentifier user, string pushRequestName, EntityIdentifier entityIdentifier = null)
 {
     AsyncHelper.RunSync(() => pushRequestSubscriptionManager.UnsubscribeAsync(user, pushRequestName, entityIdentifier));
 }