fix: throw JsonSyntaxException for null elements in AtomicIntegerArray

[priyadarshnisundararajan]

What

new Gson().fromJson("[1,null,3]", AtomicIntegerArray.class) threw a raw IllegalStateException ("Expected an int but was NULL") instead of JsonSyntaxException.

Why

In TypeAdapters.ATOMIC_INTEGER_ARRAY.read(), in.nextInt() was called directly inside a try block that only caught NumberFormatException. A JSON null token makes nextInt() throw IllegalStateException, which escaped uncaught.

Fix

Mirrors the already-merged AtomicLongArray fix from PR #3038: peek for a NULL token before reading each element and throw JsonSyntaxException("null is not a valid AtomicIntegerArray element; at path " + in.getPath()). in.getPath() (not getPreviousPath()) is used because the null token has not been consumed yet, which yields the identical $[1] path format as the AtomicLongArray fix.

Fixes #3047

Tests

Added testAtomicIntegerArrayWithNullElement to JavaUtilConcurrentAtomicTest, asserting JsonSyntaxException with message null is not a valid AtomicIntegerArray element; at path $[1] (mirrors testAtomicLongArrayWithNullElement). Ran the full JavaUtilConcurrentAtomicTest class: 9 tests, all passing (8 existing + 1 new). Maven could not resolve build extensions over this network (TLS interception on repo.maven.apache.org), so tests were compiled and run directly with javac/java 21 using jars fetched from Maven Central (junit 4.13.2, truth 1.4.5, guava 33.7.0-jre + transitive deps).

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[Marcono1234]

Thanks for the pull request! However, have you verified that the issue you are trying to fix here even existed in the first place, and have you read the discussion in #3047?

Even the author of that issue confirmed in the end that the claimed issue does not actually exist: #3047 (comment)

[priyadarshnisundararajan]

You're right, thank you for checking. I verified against current main and the reported crash does not reproduce: Gson.fromJson(JsonReader, TypeToken) already catches the IllegalStateException and wraps it as JsonSyntaxException, so there is no uncaught exception here. Closing this as invalid, apologies for the noise.