Unhandled exception. TrackSet<T>.RemoveAllUnits()

[InuInu2022]

TrackSet<T>.RemoveAllUnits()

//remove template track data
//tr.RemoveAllUnits();	//TODO:fix bug
tr.RawUnits.ForEach(u => u.Remove()); // correct

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at LibSasara.Model.CeVIOFileBase.<>c__DisplayClass6_0.<GetTrackSet>b__1(XElement e) in D:\cevio\CeVIOVoiceLibDB\tools\libs\LibSasara\LibSasara\Model\CcsProject.cs:line 146
   at System.Linq.Enumerable.WhereListIterator`1.ToList()
   at LibSasara.Model.CeVIOFileBase.GetTrackSet(Guid id) in D:\cevio\CeVIOVoiceLibDB\tools\libs\LibSasara\LibSasara\Model\CcsProject.cs:line 144
   at LibSasara.Model.CeVIOFileBase.DuplicateAndAddTrackSetAsync(Guid targetId, Nullable`1 newId) in D:\cevio\CeVIOVoiceLibDB\tools\libs\LibSasara\LibSasara\Model\CcsProject.cs:line 243