presto-main/src/main/java/io/prestosql/operator/aggregation/state/DoubleHistogramStateSerializer.java/DoubleHistogramStateSerializer/serialize
class DoubleHistogramStateSerializer:    @Override
    public void serialize(DoubleHistogramAggregation.State state, BlockBuilder out)
    {
        if (state.get() == null) {
            out.appendNull();
        }
        else {
            VARBINARY.writeSlice(out, state.get().serialize());
        }
    }