vs 2017 -> add new scaffold item -> error

Hello all,

I work with visual studio 2017 and i have just a new solution created since this monday :)

this solution contains a web project in net core 2.1

I have created a models (students / courses / )and i'm trying to add a scaffold ..

this sample must to be use for discover azure for a while and see advantage ...

I have a problem when I add a scaffold item.

I select new api controller with action entity framework 

after i select students, create new data context class 

controller name -> studentsController

but each time I have this error -> 

there were an error running the selected code generator

object reference not set to an instance of an object 

Someone has an idea about this error ?

thanks for all