Cannot retrieve a helper type for generic public type ICollection

**Describe the bug**
The exception is thrown after calling `FirstOrDefault` on the value returned by `VisualTreeHelper.FindElementsInHostCoordinates`.

**To Reproduce**
```csharp
var elements = VisualTreeHelper.FindElementsInHostCoordinates(...);
var first = elements.FirstOrDefault();
```

**Version Info**
2.1.1