in src/main/scala/org/apache/spark/sql/datasketches/theta/aggregate/ThetaSketchAggBuild.scala [159:164]
override def eval(wrapper: ThetaSketchWrapper): Any = {
val result = wrapper.serialize()
if (result != null) return result
if (nullable) return null
UpdateSketch.builder().setSeed(seed).build().compact().toByteArrayCompressed()
}