Steps to reproduce:

1. Login to back office.
2. Go to Content / Content structure.
3. Being on Landing page view (tab view) click on edit button on the left side menu.
4. Click on "Delete draft" button on the left side menu.

Actual result:

See attachment and watch gif please.

Link: https://recordit.co/eAHhG2RpsH

After clicking on "Delete draft" button an error code 500 internal server error occur.

Expected result:

User should be able to delete draft version of landing page.