AsUnion returns a [CustomChartsSectionChartsUnion] interface which you can cast.
func (r CustomChartsSectionChart) AsUnion() CustomChartsSectionChartsUnionAsUnion returns a [CustomChartsSectionChartsUnion] interface which you can cast to the specific types for more type safety.
Possible runtime types of the union are [CustomChartsSectionChartsSingleCustomChartResponseSerialized], [CustomChartsSectionChartsCustomTextBlock].