Not able to export a scene

I am using Assimp Libs v4.1.0, but I also tried v3.3.1 and 3.3.2.

I can't export a scene. I also tried to import an scene and export it withut tuching it.
But It doesn't work.

Here a code that I have tested and failed:

```
Dim mdl As Scene = Nothing
Dim ac As New AssimpContext
Dim channelIndicies As New Dictionary(Of Material, Integer)

ac.SetConfig(New Configs.NormalSmoothingAngleConfig(66.0F))
mdl = ac.ImportFile(fileName, PostProcessPreset.TargetRealTimeMaximumQuality Or PostProcessSteps.Triangulate)

Dim formatID As String = ""
Dim myExt As String = Path.GetExtension(fileName).ToLower.Substring(1)
For Each efd As ExportFormatDescription In ac.GetSupportedExportFormats
If myExt = efd.FileExtension Then
formatID = efd.FormatId
Exit For
End If
Next

ac.ExportFile(mdl, fileName, formatID, PostProcessPreset.TargetRealTimeMaximumQuality)
```

What I do wrong? Or is that a bug?

Please help me!

Reproduce the report with the supplied AssimpContext.ImportFile, GetSupportedExportFormats, and ExportFile calls using the stated Assimp versions. Start by capturing the failure details and checking the selected format ID and output path; done means identifying the cause of the failed export or documenting the missing information needed to diagnose it.

Written by the indexing model from the issue text.