a little more flexibility

[Thyra]

It would be possible to allow rows to contain fewer fields in a specific fieldGroup than are present in the header (e.g. not all Characteristics have a Term Accession or not all ParameterValues have a Unit) instead of requiring them to be empty/null as currently.
This would require changing the type of the fields from <String, String[]> to <String, HashMap<String, String>> and re-implementing the writeLine functions etc.
Also don't forget to evaluate the effect this might have on performance and whether it is worth it.