empty toast message on error response

When a POST request fails, the UI displays a JS alert followed by a red warning toast with no message. Ignoring the fact that the policy should save (which is captured under CIRC-846), the UI should handle save-errors more elegantly.

Steps to Reproduce:

1. Log into https://bugfest-goldenrod.folio.ebsco.com/
2. Go to Settings>Circulation>Loan Policies
3. Create a new Loan Policy
4. Make item Loanable, but not Renewable
   • Set Loan Profile to 'Rolling'
   • Set Loan Period to something
   • Set Fixed due date schedule (due date limit) to 'Includes today'
   • Set Closed library due date management to 'Keep the current due date'
5. Click on Save & close button

Expected Results:
New Loan Policy is saved
Green success 'toast' appears

Actual Results:
New Loan Policy is not saved
Instead, this error appears...

...and after clicking the OK button twice, the empty red 'toast' appears...

Additional Information: