fix(reader): preserve Null flag when nullable appears before type in V3.0/V3.1/V3.2 deserializers

[Copilot]

The V3.1/V3.2 schema deserializer's "type" handler unconditionally overwrote o.Type, discarding any JsonSchemaType.Null flag already set by a preceding "nullable": true handler. Result: nullable: true was silently dropped whenever it appeared before type in the document.

Description

Key-order bug in OpenApiV31Deserializer (and V32): the "nullable" handler sets o.Type = JsonSchemaType.Null when type is unknown, but the "type" handler then does a direct assignment, erasing it. V3.0 is unaffected by the production code bug — it applies nullable as a post-processing step after all keys are parsed, making it inherently order-independent.

Before:

"type", (o, n, doc) =>
{
    if (n is ValueNode)
        o.Type = n.GetScalarValue()?.ToJsonSchemaType(); // overwrites Null flag
    ...
}

After:

"type", (o, n, doc) =>
{
    var preserveNull = o.Type.HasValue && o.Type.Value.HasFlag(JsonSchemaType.Null);
    if (n is ValueNode)
    {
        var parsedType = n.GetScalarValue()?.ToJsonSchemaType();
        o.Type = preserveNull ? parsedType | JsonSchemaType.Null : parsedType;
    }
    ...
}

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Changes Made

• V31/OpenApiSchemaDeserializer.cs: "type" handler now checks for an existing Null flag (set by a preceding nullable: true) and preserves it via bitwise OR for both scalar and array type values
• V32/OpenApiSchemaDeserializer.cs: same fix applied
• V31Tests/OpenApiSchemaTests.cs: added parameterized test asserting nullable before or after type both yield JsonSchemaType.String | JsonSchemaType.Null
• V3Tests/OpenApiSchemaTests.cs: same test duplicated for OpenAPI 3.0
• V32Tests/OpenApiSchemaTests.cs: same test duplicated for OpenAPI 3.2

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• All existing tests pass

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Versions applicability

• My change applies to the version 1.X of the library, if so PR link:
• My change applies to the version 2.X of the library, if so PR link:
• My change applies to the version 3.X of the library, if so PR link:
• I have evaluated the applicability of my change against the other versions above.

Additional Notes

The V3.0 deserializer is not affected by the production code bug — it applies nullable as a deferred post-processing step after all keys have been parsed, making it inherently order-independent. Tests for V3.0 were added to confirm this behaviour is and remains correct.

[baywet]

@copilot duplicate the test for 3.0 and 3.2 as well

[Copilot]

@copilot duplicate the test for 3.0 and 3.2 as well

Done in de72b1d — added the same ParseSchemaWithNullableBeforeOrAfterTypePreservesNullFlag theory test to V3Tests/OpenApiSchemaTests.cs (3.0) and V32Tests/OpenApiSchemaTests.cs (3.2), covering both key orderings in each version.

[baywet]

do not merge before #2854 has been merged and published.

[sonarqubecloud]

Quality Gate failed

Failed conditions
21.7% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud