presto-kudu/src/main/java/io/prestosql/plugin/kudu/KuduRecordCursor.java/KuduRecordCursor/isNull
class KuduRecordCursor:    @Override
    public boolean isNull(int field)
    {
        int mappedField = mapping(field);
        return mappedField >= 0 && currentRow.isNull(mappedField);
    }