There is some problem when I inherit ColorMaterialProperty in typescript file

CesiumJS
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Before this I successfully inherit Material (CustomColorTypeMaterial) in TS file and use in Primitive.

CustomColorMaterialProperty.ts

export class CustomColorMaterialProperty extends ColorMaterialProperty

MaterialProperty can not be inherited, So I inherit ColorMaterialProperty.
Override method getType:

 public getType(time: JulianDate): string {
    return "CustomColorType";
  }

Bussiness.ts

entities.add({
      polyline: {
        positions: Cartesian3.fromDegreesArray(lineConcat),
        material: new CustomColorMaterialProperty (),
      },
    });

I found that getType is never called. And custom styles were not applied successfully.

how to inherit MaterialProperty (CustomColorMaterialProperty.ts) and use in Entity.