Class Empty

src/main/java/graphql/execution/Async.java:87–120

    }

    private static class Empty<T> implements CombinedBuilder<T> {

        private int ix;

        @Override
        public void add(CompletableFuture<T> completableFuture) {
            this.ix++;
        }

        @Override
        public void addObject(Object object) {
            this.ix++;
        }

        @Override
        public CompletableFuture<List<T>> await() {
            assertTrue(ix == 0, "expected size was 0 got %d", ix);
            return typedEmpty();
        }

        @Override
        public Object awaitPolymorphic() {
            Assert.assertTrue(ix == 0, () -> "expected size was " + 0 + " got " + ix);
            return Collections.emptyList();
        }

        // implementation details: infer the type of Completable<List<T>> from a singleton empty
        private static final CompletableFuture<List<?>> EMPTY = CompletableFuture.completedFuture(Collections.emptyList());

        @SuppressWarnings("unchecked")
        private static <T> CompletableFuture<T> typedEmpty() {
            return (CompletableFuture<T>) EMPTY;
        }
    }

    private static class Single<T> implements CombinedBuilder<T> {