### Steps to reproduce

1. Login as an admin

2. Begin of the insertionE.g have a document created under some document category (works similarly for the other enumerations)

3. End of the insertion Go to Administration > Enumerations

Begin of the insertion4.End of the insertion Begin of the deletion 3.End of the deletion Open Begin of the insertiontheEnd of the insertion Begin of the deletion any existingEnd of the deletion enumeration Begin of the insertionof which a document has been uploadedEnd of the insertion

Begin of the insertion5.End of the insertion Begin of the deletion 4.End of the deletion Click on Delete


### What is the buggy behavior?

* Nothing happens


### What is the expected behavior?

1. Begin of the insertionUser should either:

1. See an error message stating why the enumeration cannot beEnd of the insertion Begin of the deletion Enumeration is successfullyEnd of the deletion deleted Begin of the insertionOR

End of the insertion Begin of the deletion

End of the deletion 2. Begin of the insertionBe asked to what alternative enumeration the existing entries should be moved


End of the insertion Begin of the deletion User sees confirmation message


End of the deletion ### Screenshots and other files

<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/240953/content">

### Environment information

**OpenProject version**

_15.0_

**Browser**

* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Chrome
* [x] Firefox
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion Safari
* [ ] Mobile Safari
* [ ] Other (please specify)

**Operating System**

* [x] Windows
* [ ] Mac OS X
* [ ] Mobile iOS
* [ ] Mobile Android
* [ ] Linux (please specify distro)
* [ ] Chrome OS
* [ ] Other (please specify)