NullReferenceException in ApiVersionParameterDescriptionContext.RemoveAllParametersExcept

[dbrink]

When using the ApiExplorer in AspNet Core a null reference exception is thrown if the API defines a parameter as part of a route, but does not have matching parameter on the controller method.

[HttpGet("foo/{unmatched}"]
public string GetFoo()
{
   return "foo";
}

With no matching C# parameter on GetFoo() the ApiParameterDescription's ModelMetadata is null. A null coalescing operator should fix the problem.

void RemoveAllParametersExcept( ApiParameterDescription parameter )
{
// code omitted
   if ( otherParameter?.ModelMetadata.DataTypeName == nameof( ApiVersion ) )
   {
      collection.Remove( otherParameter );
   }
// code omitted
}

[commonsensesoftware]

Yep ... except you want to coalesce on the model metadata like so otherParameter.ModelMetadata?.DataTypeName == nameof( ApiVersion ). It's not the parameter that's null, it's the model metadata.

I had new feature I was about to roll out for the API Explorer anyway. I should have this patched and published tonight or tomorrow. Thanks.

[dbrink]

Ah, yes. Thanks for the catch and incorporating the fix.

[wburgers]

Is it possible to backport this bugfix to version 1.0.2 of Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer?

[commonsensesoftware]

It's possible, but kind of a pain. Is there a particular reason to not move forward? As an army of one, it's hard to maintain multiple different version branches on 3 difference platforms. This would require creating a divergent branch with the fix or publishing a package version with the fix which doesn't correspond back to source. Neither is very amicable scenario.

[wburgers]

No, there is no particular reason.
We just lag behind in our asp.net core maintenance 😇.
I'll see if I can upgrade our webapp.
Thanks for getting back to me!