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fix: kotlin nullable composed schema #3381

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fix: kotlin nullable composed schema #3381

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0cb12af
test: cover nullable composed Kotlin properties
itd-sw Oct 8, 2026
c1d9e46
fix: preserve nullability of composed Kotlin properties
itd-sw Oct 8, 2026
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17 changes: 12 additions & 5 deletions ...r-common/src/main/java/org/springdoc/core/customizers/KotlinNullablePropertyCustomizer.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -127,7 +127,7 @@ class KotlinNullablePropertyCustomizer(
/**
* Marks a non-$ref property as nullable.
* - OAS 3.0: `nullable: true`
* - OAS 3.1: adds `"null"` to the `types` set
* - OAS 3.1: adds `"null"` to the `types` set, or to `oneOf` for a composed schema
*
* A schema representing `Any?` carries no `type`/`types` constraint, i.e. it is an
* "any" schema which already permits any value including `null`. Such a schema is left
Expand All @@ -138,9 +138,15 @@ class KotlinNullablePropertyCustomizer(
if (isAnySchema(property)) return

if (specVersion == SpecVersion.V31) {
val currentTypes = property.types ?: property.type?.let { setOf(it) } ?: emptySet()
if ("null" !in currentTypes) {
property.types = currentTypes + "null"
if (!property.oneOf.isNullOrEmpty()) {
if (property.oneOf.none { it.type == "null" || "null" in (it.types ?: emptySet()) }) {
property.oneOf = property.oneOf + Schema<Any>().apply { addType("null") }
}
} else {
val currentTypes = property.types ?: property.type?.let { setOf(it) } ?: emptySet()
if ("null" !in currentTypes) {
property.types = currentTypes + "null"
}
}
} else {
property.nullable = true
Expand All @@ -155,7 +161,8 @@ class KotlinNullablePropertyCustomizer(
private fun isAnySchema(property: Schema<*>): Boolean =
property.`$ref` == null &&
property.type == null &&
property.types.isNullOrEmpty()
property.types.isNullOrEmpty() &&
property.oneOf.isNullOrEmpty()

/**
* Wraps a $ref property in a nullable composite schema. A fresh wrapper schema is returned
Expand Down
7 changes: 7 additions & 0 deletions ...otlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v30/app18/NullableController.kt
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Expand Up @@ -11,13 +11,20 @@ data class NullableFieldsResponse(
val nullableAny: Any? = null,
@field:Schema(description = "The nested object")
val nullableNested: NestedObject? = null,
val nullableComposed: ComposedObject? = null,
)

data class NestedObject(
val name: String,
val description: String? = null,
)

sealed class ComposedObject {
data class First(val first: String) : ComposedObject()

data class Second(val second: String) : ComposedObject()
}

@RestController
class NullableController {
@GetMapping("/nullable")
Expand Down
7 changes: 7 additions & 0 deletions ...otlin-webmvc-tests/src/test/kotlin/test/org/springdoc/api/v31/app23/NullableController.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -11,13 +11,20 @@ data class NullableFieldsResponse(
val nullableAny: Any? = null,
@field:Schema(description = "The nested object")
val nullableNested: NestedObject? = null,
val nullableComposed: ComposedObject? = null,
)

data class NestedObject(
val name: String,
val description: String? = null,
)

sealed class ComposedObject {
data class First(val first: String) : ComposedObject()

data class Second(val second: String) : ComposedObject()
}

@RestController
class NullableController {
@GetMapping("/nullable")
Expand Down
52 changes: 52 additions & 0 deletions ...i-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.0.1/app18.json
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,28 @@
},
"components": {
"schemas": {
"ComposedObject": {
"type": "object"
},
"First": {
"required": [
"first"
],
"type": "object",
"allOf": [
{
"$ref": "#/components/schemas/ComposedObject"
},
{
"type": "object",
"properties": {
"first": {
"type": "string"
}
}
}
]
},
"NestedObject": {
"required": [
"name"
Expand Down Expand Up @@ -79,8 +101,38 @@
"$ref": "#/components/schemas/NestedObject"
}
]
},
"nullableComposed": {
"nullable": true,
"oneOf": [
{
"$ref": "#/components/schemas/First"
},
{
"$ref": "#/components/schemas/Second"
}
]
}
}
},
"Second": {
"required": [
"second"
],
"type": "object",
"allOf": [
{
"$ref": "#/components/schemas/ComposedObject"
},
{
"type": "object",
"properties": {
"second": {
"type": "string"
}
}
}
]
}
}
}
Expand Down
50 changes: 50 additions & 0 deletions ...i-tests/springdoc-openapi-kotlin-webmvc-tests/src/test/resources/results/3.1.0/app23.json
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,25 @@
},
"components": {
"schemas": {
"ComposedObject": { },
"First": {
"allOf": [
{
"$ref": "#/components/schemas/ComposedObject"
},
{
"type": "object",
"properties": {
"first": {
"type": "string"
}
}
}
],
"required": [
"first"
]
},
"NestedObject": {
"type": "object",
"properties": {
Expand Down Expand Up @@ -81,11 +100,42 @@
"type": "null"
}
]
},
"nullableComposed": {
"oneOf": [
{
"$ref": "#/components/schemas/First"
},
{
"$ref": "#/components/schemas/Second"
},
{
"type": "null"
}
]
}
},
"required": [
"requiredField"
]
},
"Second": {
"allOf": [
{
"$ref": "#/components/schemas/ComposedObject"
},
{
"type": "object",
"properties": {
"second": {
"type": "string"
}
}
}
],
"required": [
"second"
]
}
}
}
Expand Down