oapi-codegen · mromaszewicz · Jul 6, 2026 · Jul 6, 2026
@@ -0,0 +1,8 @@
+---
+# yaml-language-server: $schema=../../../../configuration-schema.json
+package: issue2430
+output: issue2430.gen.go
+generate:
+  models: true
+output-options:
+  skip-prune: true
@@ -0,0 +1,3 @@
+package issue2430
+
+//go:generate go run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen --config=config.yaml spec.yaml
@@ -0,0 +1,37 @@
+package issue2430
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Regression test for https://github.com/oapi-codegen/oapi-codegen/issues/2430.
+//
+// OpenAPI 3.1 allows a schema whose only type is "null" (as opposed to a
+// type array that merely includes "null"). Such a schema validates exactly
+// the JSON value null. The generator used to fail with "unhandled Schema
+// type: &[null]"; it now maps the schema to `any`, with no optional
+// pointer, since nil is already `any`'s zero value.
+
+func TestNullTypePropertyRoundTrip(t *testing.T) {
+	var v ChallengeOpenJson
+	require.NoError(t, json.Unmarshal([]byte(`{"id":"1","challenger":null}`), &v))
+	assert.Equal(t, "1", v.Id)
+	assert.Nil(t, v.Challenger)
+
+	out, err := json.Marshal(RequiredNull{})
+	require.NoError(t, err)
+	// The required null-typed field must serialize as an explicit null.
+	assert.JSONEq(t, `{"value":null}`, string(out))
+}
+
+func TestNullTypeComponentIsAny(t *testing.T) {
+	// NullOnly is an alias for `any`; assigning an arbitrary value must
+	// compile, and nil round-trips through JSON as null.
+	var n NullOnly
+	require.NoError(t, json.Unmarshal([]byte(`null`), &n))
+	assert.Nil(t, n)
+}
@@ -0,0 +1,33 @@
+openapi: 3.1.0
+info:
+  title: issue-2430
+  version: 1.0.0
+paths: {}
+components:
+  schemas:
+    # A property whose schema is the bare OpenAPI 3.1 null type: the only
+    # valid JSON value for `challenger` is null. Maps to `any` in Go.
+    ChallengeOpenJson:
+      type: object
+      required:
+        - id
+      properties:
+        id:
+          type: string
+        url:
+          type: string
+          format: uri
+        challenger:
+          type: "null"
+    # A required null-typed property: must not be wrapped in a pointer,
+    # since `any` already has nil as its zero value.
+    RequiredNull:
+      type: object
+      required:
+        - value
+      properties:
+        value:
+          type: "null"
+    # A named component that is itself the bare null type.
+    NullOnly:
+      type: "null"
@@ -1186,6 +1186,18 @@ func oapiSchemaToGoType(schema *openapi3.Schema, path []string, outSchema *Schem
 			outSchema.SkipOptionalPointer = true
 		}
 		outSchema.DefineViaAlias = true
+	} else if t.Is("null") {
+		// OpenAPI 3.1 allows a schema whose only type is "null", which
+		// validates exactly the JSON value null. Go has no type whose only
+		// value is null, so map it to `any` — the same permissive mapping
+		// used for typeless schemas — rather than rejecting an otherwise
+		// valid spec. An optional pointer makes no sense for `any`, whose
+		// zero value is already nil, so skip it — mirroring the
+		// typeless-schema handling in GenerateGoSchema.
+		// See https://github.com/oapi-codegen/oapi-codegen/issues/2430
+		outSchema.GoType = "any"
+		outSchema.SkipOptionalPointer = true
+		outSchema.DefineViaAlias = true
 	} else {
 		return fmt.Errorf("unhandled Schema type: %v", t)
 	}

@@ -527,3 +527,15 @@ func TestProperty_ZeroValueIsNil(t *testing.T) {
 		})
 	}
 }
+
+// A bare OpenAPI 3.1 `type: "null"` schema validates exactly the JSON
+// value null. Go has no such type, so it maps to `any`, with the optional
+// pointer skipped (nil is already `any`'s zero value). Issue #2430.
+func TestOapiSchemaToGoType_NullType(t *testing.T) {
+	schema := &openapi3.Schema{Type: &openapi3.Types{"null"}}
+	var out Schema
+	require.NoError(t, oapiSchemaToGoType(schema, []string{"Challenger"}, &out))
+	assert.Equal(t, "any", out.GoType)
+	assert.True(t, out.SkipOptionalPointer)
+	assert.True(t, out.DefineViaAlias)
+}
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		package issue2430

		//go:generate go run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen --config=config.yaml spec.yaml