ScriptedImporter throwing exception when using AddComponent

Hello,
i'm trying to use the experimental ScriptedImporter.

code with last beta version 2017.3.0f1 (i frist tried with the 2017.2, but same bug occured)

Code (CSharp):

1. public override void OnImportAsset(AssetImportContext ctx){
2.  
3. var go = new GameObject();
4. CustomMonoBehaviour comp = go.AddComponent<CustomMonoBehaviour >();
5. ctx.AddObjectToAsset("MainAsset", go);
6. //...
7. }

when i've got the asset selected in unity , so that the inspector is shown, i got 2 exception :

and the component is not displayed in the "imported Object" section of the inspector.

not sure if i missd some step or if it's a bug.
Any help appreciated

 

not a very successful thread

did anyone else have tried the ScriptedImporter ?
Is it bad practice to AddComponent to created master gameobject ?

still struggling with this issue.