Generate nullable JSON Schema types for @Nullable members

[Hugo-DDT]

What changed

Registered a withNullableCheck in AbstractSpringAiSchemaModule so that members detected as nullable (via @Nullable annotations or Kotlin nullability, using Spring's Nullness detection) are typed to also admit null in the generated JSON Schema.

For a @Nullable String field, the schema previously emitted:

"email" : { "type" : "string" }

while also dropping email from required — producing a schema with no valid value for that property. It now emits:

"email" : { "type" : ["string", "null"] }

Why

checkRequired already treats @Nullable/Kotlin-nullable members as non-required, but nothing registered the corresponding withNullableCheck, so the generated schema was unsatisfiable for nullable properties. This mirrors the Nullness detection already used by checkRequired, and follows the KotlinModule precedent for withNullableCheck.

How verified

Updated the existing pinning test generateSchemaForTypeWithJSpecifyNullableField to assert the nullable email field is typed as ["string", "null"] while the non-nullable name field remains "string" and email stays out of required.

Related

Relates to #6950 (addresses the @Nullable half; the question of whether unannotated reference types should be nullable-by-default is left for a separate discussion).

[Copilot]

🟢 Approval recommended

Nullable schema handling is covered by the updated regression test, with no unresolved blocking issues.

Pull request overview

Updates JSON Schema generation so nullable members accept null while remaining optional.

Changes:

• Registers Spring Nullness-based nullable schema handling.
• Updates the nullable-field regression test.

File summaries

File	Description
spring-ai-model/src/test/java/org/springframework/ai/util/json/JsonSchemaGeneratorTests.java	Verifies nullable fields use ["string", "null"].
spring-ai-model/src/main/java/org/springframework/ai/util/json/schema/AbstractSpringAiSchemaModule.java	Adds nullable type detection.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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