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 EZP-25375.