return resultValue.withSideEffect(sideEffectBuilder.build());
        }
    }

    private static abstract class AbstractPlusCollector<T> implements Collector<T> {
        protected final Collector<T> left;
        protected final Collector<T> right;

        private AbstractPlusCollector(Collector<T> left, Collector<T> right) {
            this.left = left;
            this.right = right;
        }

        }
    }

    private static abstract class AbstractPlusCollector<K, V> implements MapCollector<K, V> {

        protected final MapCollector<K, V> left;
        protected final MapCollector<K, V> right;

        private AbstractPlusCollector(MapCollector<K, V> left, MapCollector<K, V> right) {
            this.left = left;
            this.right = right;