OpenApiResponseWithBody fails to serialize object

[michaelelleby]

Describe the issue
Swagger JSON fails to generate when using OpenApiResponseWithBody attribute.

To Reproduce
Steps to reproduce the behavior:

1. dotnet openapi add url https://developer.swift.com/sites/default/files/specs/Swift-Messaging-API-v1.0.0.yaml
2. Add Function with HTTP trigger and attributes [OpenApiOperation] and [OpenApiResponseWithBody(statusCode: HttpStatusCode.OK, bodyType: typeof(ListDistributionsResponse), contentType: "application/json")]
3. Open generated Swagger JSON URI at http://localhost:7097/api/swagger.json

Expected behavior
Swagger JSON is generated correctly.

Screenshots
If applicable, add screenshots to help explain your issue.

Environment (please complete the following information, if applicable):

• OS: [e.g. Windows/Mac/Linux] Windows
• Browser [e.g. edge, chrome, firefox, safari] Firefox
• Version [e.g. 22] Tried both 1.5.1 and 2.0.0-preview2

Additional context
https://github.com/michaelelleby/azure-functions-openapi-extension-bugreport is a small project demonstrating the issue.

This is the response from the Swagger JSON page:

Index was outside the bounds of the array.

   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Extensions.TypeExtensions.GetUnderlyingType(Type type)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ListObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair`2 type, NamingStrategy namingStrategy, Attribute[] attributes)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.OpenApiSchemaAcceptor.Accept(VisitorCollection collection, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ObjectTypeVisitor.ProcessProperties(IOpenApiSchemaAcceptor instance, String schemaName, Dictionary`2 properties, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair`2 type, NamingStrategy namingStrategy, Attribute[] attributes)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.OpenApiSchemaAcceptor.Accept(VisitorCollection collection, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ListObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair`2 type, NamingStrategy namingStrategy, Attribute[] attributes)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.OpenApiSchemaAcceptor.Accept(VisitorCollection collection, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ObjectTypeVisitor.ProcessProperties(IOpenApiSchemaAcceptor instance, String schemaName, Dictionary`2 properties, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair`2 type, NamingStrategy namingStrategy, Attribute[] attributes)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.OpenApiSchemaAcceptor.Accept(VisitorCollection collection, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.DocumentHelper.GetOpenApiSchemas(List`1 elements, NamingStrategy namingStrategy, VisitorCollection collection)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Build(Assembly assembly, OpenApiVersionType version)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.OpenApiTriggerFunctions.RenderSwaggerDocument(OpenApiHttpTriggerContext openApiContext, HttpRequest req, String extension, ExecutionContext ctx, ILogger log)

Removing the line [OpenApiResponseWithBody(statusCode: HttpStatusCode.OK, bodyType: typeof(ListDistributionsResponse), contentType: "application/json")] makes the problem go away, however I need this to make the return type of the API available to users.

[Trimatix]

potential duplicate of #313