EF return null for some but EF Core return 0

I migrate a site ASP.NET MVC to ASP.NET MVC core, with EF to EF Core.

I make a request with empty value :

 var q = bd.Prod
           .Where(o => o.xxx == yyy)
           .GroupBy(o => o.sss)
           .Select(g => new
           {
               ccc = g.Key,
               vvv = g.Sum(i => i.qqq),
               bbb = g.Sum(i => i.fff),
               nnn = g.Sum(i => i.ggg),
           });

When I execute this code with EF return null when all cell of sum are empty. But EF Core return 0 when all cell of sum are empty. How to make EF Core return null ?