LINQ не переводит FirstOrDefault() на язык SQL. Работает, если там поставить Count()

using (ApplicationContext db = new ApplicationContext())
{

    outputForm myForm = new outputForm();

    var list = db.Penalties.GroupBy(key => key.IdDriversNavigation.FullName,
                                       record => record.IdTraficCopNavigation.FullName,
                                       (key, record) => new
                                       {
                                           driver = key,
                                           traficCop = record.FirstOrDefault()
                                       });

    myForm.myGrid.DataSource = list.ToList();

    myForm.Show();
}

************** Текст исключения **************

System.InvalidOperationException: The LINQ expression '(GroupByShaperExpression:
KeySelector: (d.FullName), 
ElementSelector:(ProjectionBindingExpression: EmptyProjectionMember)
)
    .FirstOrDefault()' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.