fix: OAS 3.1 schema generation for raw Object properties

[xeulbn]

Pull Request

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Description

Related issue: #4682
This PR fixes an issue in OpenAPI 3.1 schema generation where properties
declared as raw Java Object were rendered as an empty schema ({}).

In the OAS 3.1 path, PrimitiveType.OBJECT#createProperty31() returned an empty
JsonSchema without populating Schema#types. Since OpenAPI 3.1 relies on
JSON Schema semantics and uses types during serialization, the missing type
information caused the schema to be emitted as {}.

To resolve this, the OAS 3.1 schema generation for raw Object types has been
updated to explicitly set types = ["object"].

Additionally, regression tests have been added to cover:

• raw Object properties
• List<Object> item schemas
• Map<String, Object> additionalProperties schemas

Fixes: #4682

Type of Change

• 🐛 Bug fix
• 🧪 Tests

Checklist

• I have added/updated tests as needed
• The PR title is descriptive
• The code builds and passes tests locally
• I have linked related issues (if any)

Screenshots / Additional Context

The tests were executed locally with:

mvn -pl modules/swagger-core -Dtest=ObjectFieldOas31ReproTest test

Before (OAS 3.1)

After (OAS 3.1)

[daniel-kmiecik]

@xeulbn please also check for errors in builds and code scanning jobs.

[xeulbn]

Sorry I missed the comment before the build test.
I’ll check the build results and update the commit accordingly.

[xeulbn]

The build failure was caused by the updated OAS 3.1 handling for raw Object, which changes the expected YAML output in ModelResolverOAS31Test:

• status type: [string, number] → [object, string, number]
• extraObject: {} → { type: object }

I updated the OAS 3.1 expected output accordingly.

Verified locally on JDK 17 with:
mvn -pl modules/swagger-core test

All tests passed.
Thanks for the review and the helpful feedback!