InvalidOperationException

[chanming9]

i had the following issue on importing the files:

InvalidOperationException: Nullable object must have a value.
System.Nullable`1[T].get_Value () (at <c2a97e0383e8404c9fc0ae19d58f57f1>:0)
Siccity.GLTFUtility.GLTFAnimation.Import (Siccity.GLTFUtility.GLTFAccessor+ImportResult[] accessors, Siccity.GLTFUtility.GLTFNode+ImportResult[] nodes, Siccity.GLTFUtility.ImportSettings importSettings) (at Assets/GLTFUtility-master/Scripts/Spec/GLTFAnimation.cs:86)
Siccity.GLTFUtility.GLTFAnimationExtensions.Import (System.Collections.Generic.List`1[T] animations, Siccity.GLTFUtility.GLTFAccessor+ImportResult[] accessors, Siccity.GLTFUtility.GLTFNode+ImportResult[] nodes, Siccity.GLTFUtility.ImportSettings importSettings) (at Assets/GLTFUtility-master/Scripts/Spec/GLTFAnimation.cs:231)
Siccity.GLTFUtility.Importer.LoadInternal (Siccity.GLTFUtility.GLTFObject gltfObject, System.String filepath, System.Byte[] bytefile, System.Int64 binChunkStart, Siccity.GLTFUtility.ImportSettings importSettings, UnityEngine.AnimationClip[]& animations) (at Assets/GLTFUtility-master/Scripts/Importer.cs:219)
Siccity.GLTFUtility.Importer.ImportGLB (System.String filepath, Siccity.GLTFUtility.ImportSettings importSettings, UnityEngine.AnimationClip[]& animations) (at Assets/GLTFUtility-master/Scripts/Importer.cs:73)
Siccity.GLTFUtility.Importer.LoadFromFile (System.String filepath, Siccity.GLTFUtility.ImportSettings importSettings, UnityEngine.AnimationClip[]& animations, Siccity.GLTFUtility.Format format) (at Assets/GLTFUtility-master/Scripts/Importer.cs:34)
Siccity.GLTFUtility.Importer.LoadFromFile (System.String filepath, Siccity.GLTFUtility.Format format) (at Assets/GLTFUtility-master/Scripts/Importer.cs:18)