RadialGradient constructor Null safety
Implementation
const factory RadialGradient(
    {final Alignment center,
    final double radius,
    required final List<Color> colors,
    final List<double>? stops,
    final TileMode tileMode,
    final Alignment? focal,
    final double focalRadius,
    final GradientTransform? transform}) = _$RadialGradient;