presto-main/src/main/java/io/prestosql/operator/unnest/ArrayOfRowsUnnester.java/ArrayOfRowsUnnester/appendNulls
class ArrayOfRowsUnnester:    @Override
    public void appendNulls(int count)
    {
        for (int i = 0; i < count; i++) {
            for (int field = 0; field < fieldCount; field++) {
                getBlockBuilder(field).appendNull();
            }
        }
    }