### Steps to reproduce

1. Login as an admin Begin of the insertionon qa.openproject-stage.comEnd of the insertion

2. Under Administration Begin of the deletion  > Custom FieldEnd of the deletion > Work Begin of the deletion package tab, create a CF of type WIL and add it to your test project

3. Under Administration > WorkEnd of the deletion packages > Types, open any type and go to tab Form configuration

Begin of the insertion3.End of the insertion Begin of the deletion 4.End of the deletion Add Begin of the insertionanyEnd of the insertion Begin of the deletion your newly created WPEnd of the deletion CF Begin of the insertionto any sectionEnd of the insertion Begin of the deletion of type WILEnd of the deletion

Begin of the insertion4.End of the insertion Begin of the deletion 5.End of the deletion Save


### What is the buggy behaviour?

* 500 is thrown


### What is the expected behaviour?

1. No 500 Begin of the insertion


### Additional information

* After refreshing the url, the form actually IS updated, so the error happens AFTER the change is persisted

* This somehow does not happen on every type, but can be observed on [type 1](https://qa.openproject-stage.com/types/1/form_configuration/edit) End of the insertion


###

### Screenshots and other files

<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/917536/content">

### Environment information

**OpenProject version**

Core build

[b8559720c86b043584d6ffd4e91a91dd8e7a8a34](https://github.com/opf/openproject/commits/b8559720c86b043584d6ffd4e91a91dd8e7a8a34)

Product version

[bc8f10aeb0ace1a06043a488d9972b8e6ce058f3](https://github.com/opf/saas-openproject/commits/bc8f10aeb0ace1a06043a488d9972b8e6ce058f3)

Core version

OpenProject 17.0.0

**Browser**

* [ ] Chrome
* [x] Firefox
* [ ] 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)