### What?
Assuming you have a hook in your collection that is looking for certain
conditions to be met related to the join field. The way you would
prevent it is to throw a `new ValidationError()` with errors containing
the path of the field. Previously, the error message for the field would
not show in the admin UI at all.
### Why?
Users need to be able to see any custom error messages for joins field
in the UI so they can address the issue.
### How?
Adds an error class and display the FieldError in the Join field in the
UI component.
dd28959916
