Can't save edited MR exhibit

[vjpixel]

Describe the bug
When I edit an MR Exhibition, I get error messages that avoid me to save it.

To reproduce the bug
Steps to reproduce the behavior:

1. Go to https://jandig.app/exhibits/edit-mr/?id=511
2. Edit the name and URL
3. Click Edit Exhibit (to save)

Expected behavior
Should save.

Screen captures