presto-main/src/main/java/io/prestosql/operator/aggregation/arrayagg/ArrayAggregationFunction.java/ArrayAggregationFunction/specialize
class ArrayAggregationFunction:    @Override
    public InternalAggregationFunction specialize(BoundVariables boundVariables, int arity, Metadata metadata)
    {
        Type type = boundVariables.getTypeVariable("T");
        return generateAggregation(type, groupMode);
    }