IncludeXmlCommentsFromInheritDocs is broken in Swashbuckle.AspNetCore 6.8.0

[alser]

// xml comments file generated by c# compiler, no matter the contents (with or w/o inheritdocs)
const string xmlFilePath = "path/to/MyAssembly.xml";

services.AddSwaggerGen(options =>
{
    options.IncludeXmlComments(xmlFilePath);
    options.IncludeXmlCommentsFromInheritDocs();
});

Call to IncludeXmlCommentsFromInheritDocs fails with the exception below.

System.ArgumentNullException: Value cannot be null. (Parameter 'source')
   at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Boolean& found)
   at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
   at Unchase.Swashbuckle.AspNetCore.Extensions.Extensions.SwaggerGenOptionsExtensions.<>c.<IncludeXmlCommentsFromInheritDocs>b__7_1(FilterDescriptor x)
   at System.Linq.Enumerable.WhereSelectListIterator`2.MoveNext()
   at System.Linq.Enumerable.CastIterator[TResult](IEnumerable source)+MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Unchase.Swashbuckle.AspNetCore.Extensions.Extensions.SwaggerGenOptionsExtensions.IncludeXmlCommentsFromInheritDocs(SwaggerGenOptions swaggerGenOptions, Boolean includeRemarks, Type[] excludedTypes)

Same behavior if supplied XPathDocument:

options.IncludeXmlComments(() => new XPathDocument(new StringReader(File.ReadAllText(xmlFilePath))));

---

In Swashbuckle.AspNetCore sources method IncludeXmlComments results in calling to:

swaggerGenOptions.AddSchemaFilterInstance(new XmlCommentsSchemaFilter(xmlDocMembers));

which in turn does this:

swaggerGenOptions.SchemaFilterDescriptors.Add(new FilterDescriptor
{
    Type = typeof(TFilter),
    FilterInstance = filterInstance
});

therefore creating FilterDescriptor with Arguments = null.

Method IncludeXmlCommentsFromInheritDocs in this repo starts with:

var documents = swaggerGenOptions.SchemaFilterDescriptors.Where(x => x.Type == typeof(XmlCommentsSchemaFilter))
    .Select(x => x.Arguments.Single())
    .Cast<XPathDocument>()
    .ToList();

expecting to see single argument of type XPathDocument, but throwing ANE

[sprudel79]

Same issue on my side in this call of method IncludeXmlCommentsFromInheritDocs:

List<XPathDocument> list = (from x in swaggerGenOptions.SchemaFilterDescriptors
                                    where x.Type == typeof(XmlCommentsSchemaFilter)
                                    select x.Arguments.Single()).Cast<XPathDocument>().ToList();

It's working with Swashbuckle 6.7.3, the question of course is, if it's a bug in that library or my bad understanding of the required setup. I have compared the swaggerGenOptions.SchemaFilterDescriptors content when using the 6.7.3 version and for the types XmlCommentsSchemaFilter I can always see a populated Arguments property.

[alser]

It's working in Swashbuckle 6.7.3 for me too, and same code in my app was working since at least 6.5.0 with the same version of Unchase.Swashbuckle.AspNetCore.Extensions 2.7.1

[alser]

I've reported this issue to Swashbuckle repo, to see if it's intended or not from their side https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/3081