Throw JsonSyntaxException for null element in primitive array

[jdymitarai]

Purpose

Throw JsonSyntaxException instead of a raw IllegalArgumentException when a JSON array with a null element is deserialized into a primitive array.

Description

Deserializing a JSON array that contains a null element into any primitive array (e.g. int[], boolean[], double[], long[], char[], byte[], short[], float[]) currently causes reflection (Array.set(array, i, null)) to throw an uncaught java.lang.IllegalArgumentException:

new Gson().fromJson("[1, null, 3]", int[].class); // java.lang.IllegalArgumentException

Because IllegalArgumentException is neither wrapped nor caught, it terminates execution with a raw runtime exception and lacks any JSON document path context.

This PR adds a null check in ArrayTypeAdapter.read when componentType.isPrimitive():

1. Rejects null elements early and fails fast with JsonSyntaxException ("null is not a valid " + componentType.getName() + "[] element; at path " + in.getPreviousPath()), directly mirroring the precedent established for AtomicLongArray in Throw JsonSyntaxException instead of NullPointerException for a null AtomicLongArray element #3038 and Fix some adapter exceptions not including JSON document location #3096.
2. Accurately reports the JSON document path (e.g. $[1] or $[0][1]).
3. Leaves Object arrays (e.g. Integer[], String[], and outer dimensions of multidimensional arrays like int[][]) unaffected so they can continue to contain null elements as valid Java objects.
4. Adds comprehensive unit tests in ArrayTest covering all primitive types, boxed arrays, and multidimensional arrays.

Checklist

• New code follows the Google Java Style Guide
• New unit tests have been added
  • Assertions in unit tests use Truth
  • No JUnit 3 features are used
  • New tests added in ArrayTest for situations which failed previously and are now fixed

[Marcono1234]

Thanks! There is already an existing recent PR which fixes that issue (as well as a few related ones): #3108

Would it be ok for you if that existing PR was preferred over your one? Maybe it would be helpful if you had a look at that PR and verify that it covers everything your PR covers. The tests there are not as extensive, but maybe they suffice?

[jdymitarai]

Hi @Marcono1234,

Thanks for pointing that out! I took a close look at #3108 — it looks great and addresses the primitive array null issue cleanly along with the related collection adapters (TreeSet, ArrayDeque, PriorityQueue) and float/double number parsing.

I'm completely fine with preferring #3108 over this PR! The implementation approach in ArrayTypeAdapter is essentially identical. The only minor difference was that our tests in this PR explicitly asserted against all 8 Java primitive array types (int[], boolean[], double[], long[], char[], byte[], short[], float[]), but since componentType.isPrimitive() handles all 8 uniformly in ArrayTypeAdapter, the coverage in #3108 is more than sufficient.

Feel free to close this PR in favor of #3108. Thanks again for your review and stewardship of Gson!

[jdymitarai]

Closing in favor of #3108 as discussed above. Thank you!