/// <summary>
 /// Populates a list with all currently existing Users, irrespective of their state. (Different Users might be in different states, reflecting their registration status.) These are the users that are currently available in the SDK’s Users List.
 /// </summary>
 /// <param name="users">Returns a list of users in List format.</param>
 public void ListUsers(List <User> users)
 {
     if (users != null)
     {
         IList <UserWrapper> usersList = new List <UserWrapper>();
         mPtr.ListUsers(usersList);
         foreach (var user in usersList)
         {
             users.Add(new User(user));
         }
     }
 }