allow unitless values
Issue
ECDC-4235 https://jira.esss.lu.se/browse/ECDC-4235
Description of work
All values should have a units attribute, with an empty string "" (NX_UNITLESS) so that they don’t inherit the wrong unit
Checklist
- [Doesn't exist?] Changes have been documented in
changes.md - [N/A] Documentation has been updated in
documentationdirectory