presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/io/AccumuloRecordCursor.java/AccumuloRecordCursor/isNull
class AccumuloRecordCursor:    @Override
    public boolean isNull(int field)
    {
        checkArgument(field < columnHandles.size(), "Invalid field index");
        return serializer.isNull(fieldToColumnName[field]);
    }