c# generic parameter non nullable

Question

i am trying to write a c# function which converts an instance of a nullable type to the underlying non nullable type. it should look something like this:

public static T TryConvertNullableToNonNullable<T,Y>(Y o) where T: notnull{
   if(o==null) throw new ArgumentNullException(nameof(o));
   return (T)o;
}

How can I specify Y to be the nullable version of T? I know that i could write where Y: Nullable<T> but this does not work since T is generic. is there even a way of achieving this?

thanks