Fix invalid schema generation

The `nullable` property should not be emitted when `type` is not. Found via `https://apinotes.io/openapi-validator`.

Relates to #3649 and #3683.

Author: martincostello

src/Swashbuckle.AspNetCore.SwaggerGen/SchemaGenerator/SchemaGenerator.cs

@@ -49,9 +49,12 @@ private IOpenApiSchema GenerateSchemaForMember(
             ? GeneratePolymorphicSchema(schemaRepository, knownTypesDataContracts)
             : GenerateConcreteSchema(dataContract, schemaRepository);
 
+        bool usingAllOf = false;
+
         if (_generatorOptions.UseAllOfToExtendReferenceSchemas && schema is OpenApiSchemaReference reference)
         {
             schema = new OpenApiSchema() { AllOf = [reference] };
+            usingAllOf = true;
         }
 
         if (schema is OpenApiSchema concrete)
@@ -63,9 +66,12 @@ private IOpenApiSchema GenerateSchemaForMember(
             {
                 var requiredAttribute = customAttributes.OfType<RequiredAttribute>().FirstOrDefault();
 
-                var nullable = IsNullable(requiredAttribute, dataProperty, memberInfo);
-
-                SetNullable(concrete, nullable);
+                // "nullable" cannot be used without "type"
+                if (!usingAllOf)
+                {
+                    var nullable = IsNullable(requiredAttribute, dataProperty, memberInfo);
+                    SetNullable(concrete, nullable);
+                }
 
                 concrete.ReadOnly = dataProperty.IsReadOnly;
                 concrete.WriteOnly = dataProperty.IsWriteOnly;

test/Swashbuckle.AspNetCore.IntegrationTests/TodoClient/kiota-lock.json

@@ -1,5 +1,5 @@
 {
-  "descriptionHash": "DF0ACFCDC1F5CFB97A2DFB0E7A7BB004B889E5742C1925E797BC2A6B816489D5C9A4A8413CB3795FA45E7589D0E04D80856F3558CD656308C19DBDA9446A0712",
+  "descriptionHash": "6220470D2DBDA8D33A3A26AE0D99FD08E8CA025558CE7AF3EFA771BEE7F540049DFB9E14E28367BD30CC488F5A918670E40CF226C0C825CC163EDBFFA1CCE766",
   "descriptionLocation": "../snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=TodoApp.Program_swaggerRequestUri=v1.DotNet10_0.verified.txt",
   "lockFileVersion": "1.0.0",
   "kiotaVersion": "1.29.0",

test/Swashbuckle.AspNetCore.IntegrationTests/snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=MinimalAppWithNullableEnums.Program_swaggerRequestUri=v1.DotNet10_0.verified.txt

@@ -48,7 +48,6 @@
         "type": "object",
         "properties": {
           "child": {
-            "type": "null",
             "allOf": [
               {
                 "$ref": "#/components/schemas/Child"

test/Swashbuckle.AspNetCore.IntegrationTests/snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=MinimalAppWithNullableEnums.Program_swaggerRequestUri=v1.DotNet8_0.verified.txt

@@ -48,7 +48,6 @@
         "type": "object",
         "properties": {
           "child": {
-            "type": "null",
             "allOf": [
               {
                 "$ref": "#/components/schemas/Child"

test/Swashbuckle.AspNetCore.IntegrationTests/snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=MinimalAppWithNullableEnums.Program_swaggerRequestUri=v1.DotNet9_0.verified.txt

@@ -48,7 +48,6 @@
         "type": "object",
         "properties": {
           "child": {
-            "type": "null",
             "allOf": [
               {
                 "$ref": "#/components/schemas/Child"

test/Swashbuckle.AspNetCore.IntegrationTests/snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=TodoApp.Program_swaggerRequestUri=v1.DotNet10_0.verified.txt

@@ -420,8 +420,7 @@
                 "$ref": "#/components/schemas/TodoPriority"
               }
             ],
-            "description": "Gets or sets the optional priority of the Todo item.",
-            "nullable": true
+            "description": "Gets or sets the optional priority of the Todo item."
           }
         },
         "additionalProperties": false,

test/Swashbuckle.AspNetCore.IntegrationTests/snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=TodoApp.Program_swaggerRequestUri=v1.DotNet8_0.verified.txt

@@ -418,8 +418,7 @@
                 "$ref": "#/components/schemas/TodoPriority"
               }
             ],
-            "description": "Gets or sets the optional priority of the Todo item.",
-            "nullable": true
+            "description": "Gets or sets the optional priority of the Todo item."
           }
         },
         "additionalProperties": false,

test/Swashbuckle.AspNetCore.IntegrationTests/snapshots/VerifyTests.Swagger_IsValidJson_No_Startup_entryPointType=TodoApp.Program_swaggerRequestUri=v1.DotNet9_0.verified.txt

@@ -418,8 +418,7 @@
                 "$ref": "#/components/schemas/TodoPriority"
               }
             ],
-            "description": "Gets or sets the optional priority of the Todo item.",
-            "nullable": true
+            "description": "Gets or sets the optional priority of the Todo item."
           }
         },
         "additionalProperties": false,