How to disallow empty selection in a relation field?

[YassienW]

I currently have a field that allows you to select multiple items from another model (O2M relation).
Is there a way to add validation so the user can't save an empty selection? I want to ensure that the list has at least one item

Removing the last item should return an error on save

The field doesn't have a setting to control null values, and item validation doesn't work. I couldn't find any info on the docs or online. Help would be appreciated