Stream handling failing when using multiple filters

[korshyadoo]

Here is a method in my project where NullAway is reporting [NullAway] dereferenced expression re.getValue() is @Nullable in the second filter.

    public List<RelatedEntity> filterByRoleAndServiceSpecificationName(List<RelatedEntity> relatedEntities,SERVICE_SPECIFICATION serviceSpecName) {
        return relatedEntities.stream()
            .filter(re -> nonNull(re) && nonNull(re.getValue()) && nonNull(re.getValue().getServiceSpecification()))
            .filter(re -> serviceSpecName.value.equalsIgnoreCase(re.getValue().getServiceSpecification().getName()))
            .collect(Collectors.toList());
    }

It seems to be recognizing that re was null checked because it does not report an error on dereferencing re, but it's not recognizing that re.getValue() has been checked.

[msridhar]

Hi @korshyadoo yes this is beyond our current stream handling capabilities. I can think about how hard it would be to add; thanks for the report.

[pranavv00]

Hey @msridhar, this looks interesting.

I’d like to explore this — specifically how NullAway currently tracks nullability across stream operations.

From what I see, the limitation is that null checks in one filter lambda aren’t propagated to subsequent ones.

Would it make sense to:

• track flow-sensitive nullability across chained stream operations, or
• treat consecutive filters as a single logical flow?

Happy to dig into the codebase and experiment if this direction sounds reasonable.

[msridhar]

Looking deeper, I'm actually not sure why this doesn't already work. See this test case that works:

NullAway/nullaway/src/test/resources/com/uber/nullaway/testdata/NullAwayStreamSupportNegativeCases.java

Lines 119 to 137 in c85b66e

	private Stream<Integer> filterWithAndExpressionThenMapNullableContainer(
	Stream<NullableContainer<NullableContainer<String>>> stream) {
	return stream
	.filter(
	new Predicate<NullableContainer<NullableContainer<String>>>() {
	@Override
	public boolean test(NullableContainer<NullableContainer<String>> container) {
	return container.get() != null && container.get().get() != null;
	}
	})
	.map(
	new Function<NullableContainer<NullableContainer<String>>, Integer>() {
	@Override
	public Integer apply(NullableContainer<NullableContainer<String>> container) {
	return container.get().get().length();
	}
	});
	}

@korshyadoo can you rewrite your case with direct null checks to see if that works? What nonNull function are you calling?

[korshyadoo]

Thanks for checking, @msridhar . I'm using java.util.Objects.nonNull(), and if I change it to use != null it still gives me the error.