Create a date field with 0 as the timestamps. It's a very tricky use case as you need to be on UTC timezone and want to enter 01/01/1970 as a date.
Steps to reproduce:
- Create a contenttype with a date fieldtype
- Create a new content
- Manage to enter 01/01/1970 in utc
- Display the date, it will say it is empty.
- Edit the date, it will be empty.
Fixes should be quite similar as