RemoveHiddenDataPreview with hidden repeating group sets row values to null instead of deleting rows

[olemartinorg]

Description of the bug

When setting RemoveHiddenDataPreview to true and hiding a repeating group, it might be expected that the repeating group is deleted (i.e. that all rows disappear), but instead the rows are kept and all values (leaf nodes) in the repeating structure are set to null.

This caused problems when receiving data on the other end for at least one customer, as null values here are not valid according to the data model.

Steps To Reproduce

1. Open mat/lakselus-rapportering
2. Fill out the form, say you have at least one 'behandling'
3. Add at least one row in the 'behandlinger' repeating group
4. Regret your decision and say don't have any 'behandlinger' (thereby hiding the repeating group)
5. Submit the form
6. Observe the null-ed out rows in the data model

Additional Information

• https://altinn.slack.com/archives/C047F8FK2NQ/p1697008355300669