Preconditions:

Created Content type with selection field. Selection field contains at least two options.

Steps:

1. Log in to the back office
2. Go to Content/Content structure
3. Click Create
4. Select content type from preconditions and confirm
5. Select an option from selection field 
6. Click Publish
7. Go to Content types/Content
8. Go to edit mode of the content type from preconditions
9. Remove option selected in step 5 
10. Click Save and close
11. Go to published content item

Actual result:

Error 500 displayed: Key "1" for array with keys "0, 2, 3" does not exist.

Expected result:

UX input required. Maybe notification for user? Or any information that selected option was removed?