providing a screenshot without explaining won’t help us help you. reproduce on the playground, show us the position in which it happens, explain when it happens.
I ran into this recently. The light you are passing in cannot be a hemisphere light. Not sure if this is by design or not.
Passing in what ???
HemisphericLight
I think @bghgary meant passing a hemispheric light to a shadow generator. It is not supported indeed, only point, spot and directional lights can generate shadows.
Yes. I think maybe we should throw a more user friendly error message when someone does this.
ShadowGenerator takes only IShadowLight as an input and hemispheric is not implementing it 
so I am not to double check types again or we should do that in a lot of other places ?
Oh, I guess that’s fine then.