Treemap renders empty white box Declined - Not Valid

Treemap renders an empty white box.  Reproduceable with your demo code in a blank ASP .net core 3.1 blazor server app.

<SfTreeMap DataSource="GrowthReport"

           WeightValuePath="GDP"

           TValue="Country"></SfTreeMap>

@code {

    class Country
    {
        public string Name;
        public double GDP;
    }
    private List GrowthReport = new List {
        new Country  {Name="United States", GDP=17946 },
        new Country  {Name="China", GDP=10866 },
        new Country  {Name="Japan", GDP=4123 },
        new Country  {Name="Germany", GDP=3355 },
        new Country  {Name="United Kingdom", GDP=2848 },
        new Country  {Name="France", GDP=2421 },
        new Country  {Name="India", GDP=2073 },
        new Country  {Name="Italy", GDP=1814 },
        new Country  {Name="Brazil", GDP=1774 },
        new Country  {Name="Canada", GDP=1550 }
    };
}