/// <summary>
		/// Themes assigned to this Goal.
		/// </summary>
		public ICollection<Theme> GetThemes(ThemeFilter filter)
		{
			filter = filter ?? new ThemeFilter();
			filter.Goals.Clear();
			filter.Goals.Add(this);
			return Instance.Get.Themes(filter);
		}
 /// <summary>
 /// Child Themes of this Theme.
 /// </summary>
 public ICollection<Theme> GetChildThemes(ThemeFilter filter) {
     filter = filter ?? new ThemeFilter();
     filter.Parent.Clear();
     filter.Parent.Add(this);
     return Instance.Get.Themes(filter);
 }
		private ThemeFilter GetFilter()
		{
			ThemeFilter filter = new ThemeFilter();
			filter.Project.Add(_sandboxProject);
			return filter;
		}