After an upgrade to 2.2.0, series are not displayed in the UI because the series creation date is now mandatory

Steps to reproduce:
1. Follow the upgrade procedure
2.
3.

Actual Results:
The series are not visible in the "series" tab (all the colums are empty, but there are as many rows as series). However, they are still readable in the "Schedule" and "Upload" wizards.
Some exceptions are logged, as well as warnings that the series lack a mandatory metadatum ("created").

Expected Results:
The series should be correctly upgraded without errors

Workaround (if any):