/// <summary>
        /// Add item
        /// </summary>
        /// <param name="item">item to add</param>
        private void AddItem(ActionableObject item)
        {
            if (!item.IsActive)
            {
                if (this.last == null)
                {
                    this.first = item;
                    this.last  = item;
                }
                else
                {
                    this.last.Next = item;
                }

                item.IsActive = true;
            }
        }