NullReferenceException when trying to import FBX.

Hi, I'm getting the following exception with the latest versions for both (assimpnet and assimp)

`NullReferenceException: Object reference not set to an instance of an object
System.String.FormatHelper (System.Text.StringBuilder result, IFormatProvider provider, System.String format, System.Object[] args) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System/String.cs:1940)
System.String.Format (IFormatProvider provider, System.String format, System.Object[] args) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System/String.cs:1873)
System.String.Format (System.String format, System.Object arg0, System.Object arg1, System.Object arg2) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System/String.cs:1863)
Assimp.Material.CreateFullyQualifiedName (System.String baseName, TextureType texType, Int32 texIndex)
Assimp.MaterialProperty.get_FullyQualifiedName ()
Assimp.Material.AddProperty (Assimp.MaterialProperty matProp)
Assimp.Material.Assimp.IMarshalable.FromNative (Assimp.Unmanaged.AiMaterial& nativeValue)
Assimp.MemoryHelper.FromNativeArray[Material,AiMaterial] (IntPtr nativeArray, Int32 length, Boolean arrayOfPointers)
Assimp.Scene.Assimp.IMarshalable.FromNative (Assimp.Unmanaged.AiScene& nativeValue)
Assimp.MemoryHelper.FromNativePointer[Scene,AiScene] (IntPtr ptr)
Assimp.Scene.FromUnmanagedScene (IntPtr scenePtr)
Assimp.AssimpContext.ImportFile (System.String file, PostProcessSteps postProcessFlags)`

Any help is appreciated.

Start with Assimp.Material.CreateFullyQualifiedName and follow the material-property path shown in the trace through AssimpContext.ImportFile. Reproduce the failure with the reported FBX import and verify that the import completes without the NullReferenceException.

Written by the indexing model from the issue text.