Issues with projects not using GameCreator

[tadaki]

I would like to report an error that occurred when using this plugin (Unity).
It would be greatly appreciated if you could fix it.

If you run this plugin in a project that does not use GameCreator, you will get the following error

The type or namespace name 'GameCreator' could not be found (are you missing a using directive or an assembly reference?)

Also, if I comment out line 8 of GameCreatorInventory.cs, the error disappears, but when I import the model file, I get the following error

NullReferenceException: Object reference not set to an instance of an object
UMA.UMAData+UMARecipe.MergeMatchingOverlays () (at Assets/ExternalAssets/UMA/Core/StandardAssets/UMA/Scripts/UMAData.cs:1659)
UMA.UMATextRecipe.Save (UMA.UMAData+UMARecipe umaRecipe, UMA.UMAContextBase context) (at Assets/ExternalAssets/UMA/Core/Extensions/ DynamicCharacterSystem/Scripts/pUMATextRecipe.cs:371)
UMAConverter.UMAConverter`1[T].GenerateRaceAssets () (at Library/PackageCache/com.vwgamedev.umaconverter@d890823479/Editor/ UMAConverter.cs:317)
UMAConverter.UMAConverter`1[T].convert () (at Library/PackageCache/com.vwgamedev.umaconverter@d890823479/Editor/UMAConverter.cs:395)
UMAConverter.FBXImportPreprocessor.Convert (System.String path, UMAConverter.FBXImportPreprocessor+convertType type) (at Library/ PackageCache/com.vwgamedev.umaconverter@d890823479/Editor/FBXImportPreprocessor.cs:119)
UMAConverter.FBXImportPreprocessor.<OnPreprocessModel>b__0_0 () (at Library/PackageCache/com.vwgamedev.umaconverter@d890823479/Editor /FBXImportPreprocessor.cs:57)
UnityEditor.EditorApplication.Internal_CallDelayFunctions () (at <4f70cf68b8b24a78aa3a87c1d6120925>:0)