How to reproduce

• connect to cms
• open newsletter plugin
• open a newsletter
• open the history of this content
• if this content does not have previous versions, edit the content, save and validate

Actual behavior

• the button to restore the content is grey and disabled.

Expected behavior

• the button if enabled
• it is possible to restaore the content and validate it.

This is not working on 3.6 snapshot and on the demo (3.5.4)