5001: Add support for @Nullable annotations in OpenAPI 3.1 schemas

[zdary]

Pull Request

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Description

Enhanced schema generation by recognizing

• @nullable annotations as nullable and adding "null" to the type array in OpenAPI 3.1.
• nullable = true in schema and adding "null" to the type array in OpenAPI 3.1.

Introduced a test case to validate the behavior and ensure backward compatibility with explicit @Schema annotations.

Fixes: #5001 , #4555

Type of Change

• 🐛 Bug fix
• ✨ New feature
• ♻️ Refactor (non-breaking change)
• 🧪 Tests
• 📝 Documentation
• 🧹 Chore (build or tooling)

Checklist

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

Screenshots / Additional Context

[ronodhirSoumik]

is this loop needed?

if (annotations != null) {
    return Arrays.stream(annotations).anyMatch(annotation ->
                NULLABLE_ANNOTATIONS.contains(annotation.annotationType().getSimpleName()));
 }

[zdary]

Yes, it is. Not sure how to write it more elegant than this. Feel free to correct it, please if you prefer

[ewaostrowska]

This version here removes redundancy. The loop variable ann was never used - it was just a mechanism to trigger the stream operation

[zdary]

@ronodhirSoumik will this PR make its way to the release? If so any eta?

[ewaostrowska]

@zdary thanks for providing PR for this issue. As @ronodhirSoumik was suggesting the loop and stream was not necessary effective there so I have introduced a small change. Otherwise this is great :) Solves as well #4555 which community especially seemed to waiting for. It will make it to the next release.

[andrei-ivanov]

NULLABLE_ANNOTATIONS should be a Set for efficient contains

[pmerschmann]

this fix only worked for java native attributes (e.g. Strings). But if you are using objects and mark them with Nullable, the type "object" is somehow not being added, but being replaced by "null".

I created a seperate bug ticket for it with #5077 , but mainly the issue is visible in the following code snippets

For instance:

"foo": {
  "$ref": "#/components/schemas/Foo"
},

"Foo": {
        "type": "null",
        "properties": {
          "id": {
            "type": "string",
            "format": "uuid"
          },
}

instead of

"foo": {
  "$ref": "#/components/schemas/Foo"
  "nullable": true
},

"Foo": {
        "type": "object",
        "properties": {
          "id": {
            "type": "string",
            "format": "uuid"
          },
}