Generic Class Attribute for code generation causing 'Generic types are not valid.' during schema creation

[ploring04]

Our project has some simple class based generic attribute that will inject the boiler plate code for adding a property to a class.

[Property<LookupList>("LookupList")]

public partial class LookupListInfo
{
}

That will generate a class with this code generated inside the class

#region LookupList

LookupList _lookupList;

/// <summary>
/// 
/// </summary>
/// <name>Lookup List</name>
[Bindable(true)]
public LookupList LookupList() => _lookupList;
public LookupListInfo LookupList(kahua.kdk.hub.view.LookupList lookupList)
{
    _lookupList = lookupList;
    Properties.Properties(nameof(LookupList), lookupList?.Properties);
    OnLookupListChanged(lookupList);
    return this;
}

partial void OnLookupListChanged(LookupList lookupList);

#endregion LookupList

When this class is used as a return type in an endpoint the schema generator throws a 'Generic types are not valid.' exception during the call to ProcessResponseTypeAttributes.

[HttpGet]
public LookupListInfo GetInfo(string key)
{
    ...
}

Full stack trace

NJsonSchema.dll!NJsonSchema.Generation.JsonSchemaGenerator.ApplySchemaProcessors(NJsonSchema.JsonSchema schema, Namotion.Reflection.ContextualType contextualType, NJsonSchema.Generation.JsonSchemaResolver schemaResolver) Line 793	C#
NJsonSchema.dll!NJsonSchema.Generation.JsonSchemaGenerator.Generate<NJsonSchema.JsonSchema>(NJsonSchema.JsonSchema schema, Namotion.Reflection.ContextualType contextualType, NJsonSchema.Generation.JsonSchemaResolver schemaResolver) Line 155	C#
NJsonSchema.dll!NJsonSchema.Generation.JsonSchemaGenerator.Generate<NJsonSchema.JsonSchema>(Namotion.Reflection.ContextualType contextualType, NJsonSchema.Generation.JsonSchemaResolver schemaResolver) Line 121	C#
NJsonSchema.dll!NJsonSchema.Generation.JsonSchemaGenerator.GenerateWithReferenceAndNullability<NJsonSchema.JsonSchema>(Namotion.Reflection.ContextualType contextualType, bool isNullable, NJsonSchema.Generation.JsonSchemaResolver schemaResolver, System.Action<NJsonSchema.JsonSchema, NJsonSchema.JsonSchema> transformation) Line 291	C#
NSwag.Generation.dll!NSwag.Generation.OpenApiSchemaGenerator.GenerateWithReferenceAndNullability<NJsonSchema.JsonSchema>(Namotion.Reflection.ContextualType contextualType, bool isNullable, NJsonSchema.Generation.JsonSchemaResolver schemaResolver, System.Action<NJsonSchema.JsonSchema, NJsonSchema.JsonSchema> transformation) Line 81	C#
NSwag.Generation.dll!NSwag.Generation.Processors.OperationResponseProcessorBase.LoadDefaultSuccessResponse(System.Reflection.ParameterInfo returnParameter, string successXmlDescription, NSwag.Generation.Processors.Contexts.OperationProcessorContext context) Line 288	C#
NSwag.Generation.dll!NSwag.Generation.Processors.OperationResponseProcessorBase.ProcessOperationDescriptions(System.Collections.Generic.IEnumerable<NSwag.Generation.Processors.OperationResponseDescription> operationDescriptions, System.Reflection.ParameterInfo returnParameter, NSwag.Generation.Processors.Contexts.OperationProcessorContext context, string successResponseDescription) Line 232	C#
NSwag.Generation.dll!NSwag.Generation.Processors.OperationResponseProcessorBase.ProcessResponseTypeAttributes(NSwag.Generation.Processors.Contexts.OperationProcessorContext operationProcessorContext, System.Collections.Generic.IEnumerable<System.Attribute> responseTypeAttributes) Line 52	C#
NSwag.Generation.WebApi.dll!NSwag.Generation.WebApi.Processors.OperationResponseProcessor.Process(NSwag.Generation.Processors.Contexts.OperationProcessorContext context) Line 49	C#
NSwag.Generation.WebApi.dll!NSwag.Generation.WebApi.WebApiOpenApiDocumentGenerator.RunOperationProcessors(NSwag.OpenApiDocument document, System.Type controllerType, System.Reflection.MethodInfo methodInfo, NSwag.OpenApiOperationDescription operationDescription, System.Collections.Generic.List<NSwag.OpenApiOperationDescription> allOperations, NSwag.Generation.OpenApiDocumentGenerator generator, NSwag.OpenApiSchemaResolver schemaResolver) Line 251	C#
NSwag.Generation.WebApi.dll!NSwag.Generation.WebApi.WebApiOpenApiDocumentGenerator.AddOperationDescriptionsToDocument(NSwag.OpenApiDocument document, System.Type controllerType, System.Collections.Generic.List<System.Tuple<NSwag.OpenApiOperationDescription, System.Reflection.MethodInfo>> operations, NSwag.Generation.OpenApiDocumentGenerator swaggerGenerator, NSwag.OpenApiSchemaResolver schemaResolver) Line 218	C#
NSwag.Generation.WebApi.dll!NSwag.Generation.WebApi.WebApiOpenApiDocumentGenerator.GenerateForController(NSwag.OpenApiDocument document, System.Type controllerType, NSwag.Generation.OpenApiDocumentGenerator swaggerGenerator, NSwag.OpenApiSchemaResolver schemaResolver) Line 206	C#
NSwag.Generation.WebApi.dll!NSwag.Generation.WebApi.WebApiOpenApiDocumentGenerator.GenerateForControllersAsync(System.Collections.Generic.IEnumerable<System.Type> controllerTypes) Line 88	C#
NSwag.AspNet.Owin.dll!NSwag.AspNet.Owin.Middlewares.OpenApiDocumentMiddleware.GenerateDocumentAsync(Microsoft.Owin.IOwinContext context) Line 98	C#

The actual line of the exception is thrown here which goes deep into System.Reflection

private void ApplySchemaProcessors(JsonSchema schema, ContextualType contextualType, JsonSchemaResolver schemaResolver)
{
    ...
    var operationProcessorAttributes = contextualType
        .GetAttributes(true)
        .GetAssignableToTypeName(nameof(JsonSchemaProcessorAttribute), TypeNameStyle.Name);
    ...
}

I was trying to setup a TypeMapper which was not working so I dug into the code and realized even with a custom SchemaProcessor processor this line of code would still be called and throw the exception and there was no TypeMapper check.

I am still relatively new to NSwag so I was not sure the best way to resolve this issue.