fix: add null check to prevent API response errors (issue #13941)

[vaisshnavi7]

Issue #, if available: aws-amplify/amplify-js#13941 (comment)

Description of changes: This PR adds a null check to prevent potential errors in API response handling. The following changes have been made:

1. Implemented a null check in indexQuery.ts to handle cases where the API response data might be null.
2. Updated secondary-indexes.ts test to ensure that null data responses do not cause exceptions.
3. The changes affect the following packages:
   • integration-tests
   • data-schema

Validation: I reproduced the issue by simulating null data scenarios in the local environment, including cases with empty API responses. After applying the fix, I reran the integration tests and confirmed that the null data no longer caused errors.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[changeset-bot]

🦋 Changeset detected

Latest commit: 672ea2f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
integration-tests	Patch
@aws-amplify/data-schema	Patch

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[stocaaro]

Overall, this change looks good and makes sense. Two things.

1. Can the title of this change be made following the conventional commit format so that when we squash the change the commit message to the main repo will be conventional.
2. How was this change validated? Want to make sure we reproduced the error case and confirmed this fix with some level of validation documention added the the description before this gets merged.