[Content Editor][Back port] User cannot leave an empty required field (if it was filled with data) in a draft document

Description:

After the save as draft functionality was implemented, the user cannot leave an empty required field, which had previously data.

Steps to reproduce:

1. Create a new document which has a required Date field

2. Keep document as draft

3. Edit the draft

4. Remove the data from the required field

5. Keep draft

Expected result:

**The draft document has an empty date field

Actual result:

The previous value was saved.