public static WorkflowOptions UnregisterActivityType <T>(this WorkflowOptions options) where T : IActivity
        {
            if (!options.IsActivityRegistered <T>())
            {
                throw new InvalidOperationException("The specified activity type is not registered.");
            }

            options.ActivityDictionary.Remove(typeof(T));
            return(options);
        }
        public static WorkflowOptions AddActivity <T>(this WorkflowOptions options) where T : IActivity
        {
            if (!options.IsActivityRegistered <T>())
            {
                var activityType = typeof(T);
                options.ActivityDictionary.Add(activityType, activityType);
            }

            return(options);
        }