[Bug]: DefaultValue(null) doesn't work with nullable int

[PaulKamps]

Describe the bug

I have a few properties that are as following:

[DefaultValue(null)]
public int? Id { get; set; }

Expected behavior

I expect it to work as it did in 6.5.0 and before.
Now it crashes when loading the swagger page with the following error: The JSON value could not be converted to System.Int32.

Actual behavior

System.Text.Json.JsonException: The JSON value could not be converted to System.Int32. at System.Text.Json.ThrowHelper.ThrowJsonException_DeserializeUnableToConvertValue(Type propertyType) at System.Text.Json.JsonSerializer.UnboxOnWrite[T](Object value) at System.Text.Json.Serialization.Metadata.JsonTypeInfo1.SerializeAsObject(Utf8JsonWriter writer, Object rootValue)
at System.Text.Json.JsonSerializer.WriteStringAsObject(Object value, JsonTypeInfo jsonTypeInfo)
at Swashbuckle.AspNetCore.SwaggerGen.JsonSerializerDataContractResolver.JsonConverterFunc(Object value, Type type)
at Swashbuckle.AspNetCore.SwaggerGen.JsonSerializerDataContractResolver.<>c__DisplayClass2_0.b__1(Object value)
at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateDefaultValue(DataContract dataContract, Type modelType, Object defaultValue)
at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchemaForMember(Type modelType, SchemaRepository schemaRepository, MemberInfo memberInfo, DataProperty dataProperty)
at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.CreateObjectSchema(DataContract dataContract, SchemaRepository schemaRepository)
at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.<>c__DisplayClass11_0.b__3()
at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateReferencedSchema(DataContract dataContract, SchemaRepository schemaRepository, Func1 definitionFactory) at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateConcreteSchema(DataContract dataContract, SchemaRepository schemaRepository) at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchemaForParameter(Type modelType, SchemaRepository schemaRepository, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo) at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchema(Type modelType, SchemaRepository schemaRepository, MemberInfo memberInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateSchema(Type type, SchemaRepository schemaRepository, PropertyInfo propertyInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo) --- End of inner exception stack trace --- at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateSchema(Type type, SchemaRepository schemaRepository, PropertyInfo propertyInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBodyFromBodyParameter(ApiDescription apiDescription, SchemaRepository schemaRepository, ApiParameterDescription bodyParameter) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBody(ApiDescription apiDescription, SchemaRepository schemaRepository) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperation(ApiDescription apiDescription, SchemaRepository schemaRepository) --- End of inner exception stack trace --- at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperation(ApiDescription apiDescription, SchemaRepository schemaRepository) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperations(IEnumerable1 apiDescriptions, SchemaRepository schemaRepository)
at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePaths(IEnumerable1 apiDescriptions, SchemaRepository schemaRepository) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerDocumentWithoutFilters(String documentName, String host, String basePath) at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerAsync(String documentName, String host, String basePath) at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider) at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

Steps to reproduce

No response

Exception(s) (if any)

No response

Swashbuckle.AspNetCore version

6.6.2

.NET Version

8.0

Anything else?

No response

[martincostello]

Likely the same root cause as #2920 (comment).

[martincostello]

#2941

[billybraga]

This is a regression, could it be fixed in 6.6? Or is 6.7 expected to come out soon? 6.6 is pretty much unusable with this bug in it.

[martincostello]

There's no concrete date for 6.7.0 at present, and there's been a steady drip of changes recently so I've been waiting for things to slow. I'll look to publish something by the start of August as there's been a few asks recently.

If you want to use a version of 6.7.0 ASAP, you can consume prerelease packages from our MyGet feed.