fix GraphQL list types not nullable

[bramstroker]

Description (*)

Non-nullable list item types were not correctly reflected in the generated GraphQL schema for output object types.

For example, the following definition in schema.graphqls:

type AddProductsToWishlistOutput @doc(description: "Contains the customer's wish list and any errors encountered.") {
    wishlist: Wishlist! @doc(description: "Contains the wish list with all items that were successfully added.")
    user_errors: [WishListUserInputError!]! @doc(description: "An array of errors encountered while adding products to a wish list.")
}

Results in the following type in the stitched schema:

[WishListUserInputError]!

Instead of the expected:

[WishListUserInputError!]!

This issue affects all output object types. Input argument handling already behaved correctly.

This pull request fixes the schema generation logic to correctly preserve non-nullable list item types.

This same bug applied to tens of other types throughout the Magento GraphQL schema.

Related Pull Requests

Fixed Issues (if relevant)

1. Fixes magento/magento2#<issue_number>

Manual testing scenarios (*)

1. Retrieve the GraphQL introspection schema.
2. Verify that list fields defined as [Type!]! in schema.graphqls
   are preserved as [Type!]! in the stitched schema.
3. Without this fix, the same fields appear incorrectly as [Type]!.

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

[m2-assistant]

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[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email [email protected].

[ct-prd-pr-scan]

The security team has been informed about this pull request due to the presence of risky security keywords. For security vulnerability reports, please visit Adobe's vulnerability disclosure program on HackerOne or email [email protected].

[bramstroker]

@magento run all tests