### Steps to reproduce

1. Begin of the insertionIn an older version of OpenProject (basically before theEnd of the insertion Begin of the deletion Go to Admin → Projects →End of the deletion Project attributes Begin of the insertionwere introduced), create some custom fields for ProjectsEnd of the insertion
2. Begin of the insertionUpdate to the current version
3. End of the insertion Create a Begin of the insertionnewEnd of the insertion Project attribute in the Begin of the insertionadministrationEnd of the insertion Begin of the deletion default section "**Project attributes**"End of the deletion
Begin of the deletion 3. Take care that there are no other sections
End of the deletion 4. Go to any Begin of the insertionproject andEnd of the insertion Begin of the deletion project 
5. In the settings → Project attributesEnd of the deletion enable Begin of the insertionthatEnd of the insertion Begin of the deletion theEnd of the deletion attribute Begin of the insertion in the project settingsEnd of the insertion
Begin of the insertion5.End of the insertion Begin of the deletion 6.End of the deletion Go to the Begin of the insertionoverview pageEnd of the insertion Begin of the deletion OverviewEnd of the deletion of Begin of the insertionthatEnd of the insertion Begin of the deletion theEnd of the deletion project

### What is the buggy behavior?

* An error is shown

<img class="op-uc-image op-uc-image_inline" style="width:616px;" src="/api/v3/attachments/96673/content">

Begin of the insertion* **Technical:** All the old custom fiels have value `NULL` in the field for the `custom_field_section_id`. This leads to the overview page trying to create a `nil` section with all the old fields as children.

End of the insertion ### What is the expected behavior?

* There should be no error Begin of the insertion
* All old values should be visible in the default sectionEnd of the insertion

###

### Environment information

**OpenProject version**

_14.0_

**Browser**

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

**Language**

_German_