Exporting data to CSV using MultiValuedMap

Question

I need to export data in csv, using a dto that I previously used as import of a csv file, where the expected output format is:

name;parent1;parent2;...;parentN

and the header would be:

name;parents

where parents would cover all the N values that represent the parents of the format above.

During the import to be able to read such a file I had to create the dto (MyDataParentsImport) in this way:

@CsvBindByPosition(position = 0, required = true)
private String name;

@CsvBindAndJoinByPosition(position = "1-", elementType = String.class, mapType = ArrayListValuedHashMap.class, required = false)
private MultiValuedMap<Integer, String> mapParentsNames;

the import works as a charm, but when I try to export in csv using the same DTO, openCSV looses part of the data present in mapParentsNames. Sometimes if the map contains 3 parents, the csv output contains only 1 or 2 parents.

To add data in the Map I use this method:

private MultiValuedMap<Integer, String> convertToMap(List<String> names, int startingKey) {

    MultiValuedMap<Integer, String> pairs = new ArrayListValuedHashMap<>();

    if (names != null) {
        int key = startingKey;

        for (String name : names) {

            List<String> localNames = new ArrayList<>();
            localNames.add(name);

            pairs.putAll(key, localNames);

            key++;

        }
    }

    return pairs;

}

I write the CSV file in this way:

FileWriter writer = new FileWriter(file);

writer.append(MyDataHeader.getHeader() + "\n");

StatefulBeanToCsv<MyDataParentsImport> beanToCsv = new StatefulBeanToCsvBuilder<MyDataParentsImport>(writer)
                .withSeparator(BulkImportConstants.CUSTOM_SEPARATOR)
                .withQuotechar(CSVWriter.NO_QUOTE_CHARACTER)
                .build();

beanToCsv.write(myData);

where myData is a list of object of type of the dto I described before (MyDataParentsImport).

I'm using openCSV 5.9.

EDIT:

I did more tests: if myData is a list of one element, the export is correct, no parent missing.