code: public Collection<Story> getChildStories(StoryFilter filter) {
          filter = (filter != null) ? filter : new StoryFilter();
          filter.epic.clear();
          filter.epic.add(this);
          return getInstance().get().story(filter);
      }
docs: Stories that are immediate children of this Epic.
  
  @param filter Limit the story returned (If null, then all items
  returned).
  @return A collection stories that belong to this epic filtered by the
  passed in filter.