Nullable types support on examples

[JosueLimaG]

When using a nullable byte type on a request body example, the following response is returned with a 500 response code

Sequence contains no elements

at System.Linq.ThrowHelper.ThrowNoElementsException()
at System.Linq.Enumerable.First[TSource](IEnumerable1 source) at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.NullableObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair2 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, Dictionary2 properties, NamingStrategy namingStrategy) at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.ObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair2 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.Core.Document.Build(Assembly assembly, OpenApiVersionType version)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.OpenApiTriggerFunctionProvider.RenderSwaggerDocument(HttpRequest req, String extension, ExecutionContext ctx, ILogger log)

[choipureum]

related to: #96