Settings > Inventory. Confusing error when saving duplicate Statistical code

Overview: When testing permissions for Inventory (Testing Bugfest test case T14177) pwanninger found that a user can not add statistical codes in the BugFest environment. The same bug can be reproduced in FOLIO Snapshot (user: diku_admin, with all permissions).

Step to reproduce:

1. Login to FOLIO Snapshot, go to Settings > Inventory
2. Select Instance, Holdings, Item > Statistical codes
3. Click on the 'New' button
4. Enter a statistical code that has either the same name or type (or both) as one that already exists in the list
5. Click Save button

Expected result:
Should get an informative error message that tells you why the data wasn't saved: e.g. "Please supply a unique value." CB: I think this message should work universally, as I checked a number of different controlled vocabularies throughout settings and you seem to get this "Error on saving data" message when either:
1. Data is required but not supplied
2. Supplied data is not unique and should be

Actual result:
An error message: "Error on saving data"

Additional info:

• After changing my inputs to make them unique I was able to save the entry BUT the page then cleared out and said "No statistical codes". I had to nav away and back to see the codes (along with the newly created one) - UIIN-1081
• This repros in snapshot and Edelweiss as well as Fameflower BugFest
• This ambiguous error message appears elsewhere in Settings. For example, if I attempt to create a duplicate Institution