Bugfest. Instances can be saved with "select code" statistical code

Overview: Empty data element for Statistical code can be saved. The value is "null".

Steps to Reproduce:

1. Log into FOLIO Snapshot as user Diku_admin
2. Edit an instance and click "add statistical code"
3. Save the instance without selecting a code

Expected Results:
There will be an error message indicating that the Statistical code element, is not filled in.
The instance can not be saved with an empty statistical code data property.

Actual Results:
The instance gets a "null" statistical code added to the database

Additional Information:
URL:
Interested parties: jenncolt