###

### Steps to reproduce

1. Login and go to admin/projects/project attributes

2. Open a weighted item list

3. Click on Items Begin of the insertiontab, clickEnd of the insertion Begin of the deletion tab and add an item (just likeEnd of the deletion on Begin of the insertion**+Item** and cancelEnd of the insertion the Begin of the insertionformEnd of the insertion Begin of the deletion video)End of the deletion

4. Click on Details tab


### What is the buggy behavior?

* Error message appears and user is redirected to the custom fields index page


<img Begin of the insertionclass="image_resized op-uc-imageEnd of the insertion Begin of the deletion class=&quot;op-uc-imageEnd of the deletion op-uc-image_inline" Begin of the insertionstyle="width:767px;"End of the insertion src="/api/v3/attachments/813530/content">

### What is the expected behavior?

1. User should see the Details tab&nbsp;


###

### Environment information

**OpenProject version**

**Core build**

[2cc96ed3907cef265fdc0f2c8b34dab08378935d](https://github.com/opf/openproject/commits/2cc96ed3907cef265fdc0f2c8b34dab08378935d)

**Product version**

[ac55c5e1d21f25919a56fd3717fcdf8c16f88007](https://github.com/opf/saas-openproject/commits/ac55c5e1d21f25919a56fd3717fcdf8c16f88007)

**Core version**

OpenProject 16.6.0

**Browser**

* [x] Chrome
* [ ] Firefox
* [ ] Safari
* [ ] Mobile Safari
* [ ] Other (please specify)

**Operating System**

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