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Nullness improvements for simple core transforms - #40022

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stankiewicz merged 5 commits into
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kennknowles:Combine-nullness
Sep 29, 2026
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stankiewicz merged 5 commits into
apache:masterfrom
kennknowles:Combine-nullness

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Remove class-level blanket suppressions with targeted suppressions and code improvements.


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@github-actions github-actions Bot added the java label Sep 4, 2026
@kennknowles kennknowles changed the title Nullness improvements for Latest, Distinct, Reify, Sample Nullness improvements for simple core transforms Sep 4, 2026
TimestampedValue is immutable, so a TimestampedValue<V> is safe to use
wherever a TimestampedValue of a supertype of V is expected. Saying so
lets the nullness checker accept passing a TimestampedValue<T> where a
TimestampedValue<@nullable T> is wanted, which combiners need when their
accumulator starts out holding a null value.

This only loosens checking, so it cannot invalidate existing callers.
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kennknowles marked this pull request as ready for review September 10, 2026 20:31
Replace the blanket class-level nullness suppression with narrow,
documented suppressions on the methods that genuinely produce a null.

LatestFn's accumulator holds a null value until the first input arrives,
so it is now typed TimestampedValue<@nullable T>. That is invisible in
the public API, since Latest.combineFn() erases AccumT to a wildcard.
It relies on TimestampedValue being covariant in its value type, so that
an input can still be passed where an accumulator is expected.

No runtime changes beyond hoisting the timestamp comparison into a
private helper so that mergeAccumulators no longer routes through
addInput. The null-element check it relied on is retained.
Remove the blanket class-level nullness suppression. The representative
type of WithRepresentativeValues is genuinely optional -- expand()
already branches on it -- so annotate it rather than suppressing.

No runtime changes.
Remove the blanket class-level nullness suppression. Reifying a view in
the global window creates a single placeholder element, which is a null
Void; spell that type out rather than casting.

No runtime changes.
Remove the blanket class-level nullness suppression, keeping the
unrelated rawtypes one. AnyValueCombineFn.extractOutput returns null
when the input is empty, and OutputT is T in the public signature of
anyValueCombineFn(), so that keeps a narrow suppression.

No runtime changes.
@Test
public void testAddInputNullInput() {
thrown.expect(NullPointerException.class);
thrown.expect(IllegalArgumentException.class);

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moving away from org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull; to org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull changes exception thrown, I'm curious if this is intended. It's not something someone would normally catch, just observation.

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It is intended: it will throw IllegalArgumentException which is accurate. NPE is too generic and doesn't say who did the wrong thing. It also reads like "segfault" to a user, indicating a bug always, but sometimes it is not a bug but is because of how it was passed.

Basically checkNotNull should almost never be used, and NPE should be thrown only when you actually dereference a null, aka when you wrote bad code.

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stankiewicz merged commit 76a5371 into apache:master Sep 29, 2026
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2 participants