Concept list datatype with Required = True allows save with no value

[bferguso]

The concept-list datatype allows saving of a card with no value even if it is marked as Required. The datatype / widgets behave properly if no value is ever added to the list, however if a value is selected and then removed, the card can be saved.

Steps to Reproduce

1. Navigate to an empty card that has a node of type concept-list that is marked as required.
2. Press the card Save button. Note an error occurs stating the concept-list value is required. (Expected behaviour)
3. Select any item in the list
4. Remove all items from the list
5. Press the card Save button

Expected outcome: Error stating a value in the concept-list is required
Actual outcome: The card saves without error.

The above behaviour is consistent regarless of whether the widget is a concept-multiselect-widget or concept-checkbox-widget.

No errors are present in the browser console.

Arches Version: 7.5.0
Browser: Firefox Developer Edition
OS: OSX