docs: protected MergingWindowSet<W> getMergingWindowSet() throws Exception {
  		@SuppressWarnings("unchecked")
  		MergingWindowAssigner<? super IN, W> mergingAssigner = (MergingWindowAssigner<? super IN, W>) windowAssigner;
  		return new MergingWindowSet<>(mergingAssigner, mergingSetsState);
  	}