add a migration step for wrong used None str

[ReimarBauer]

Using the framework for versions we have to add a migration for
#2588

[anj20]

Hi @ReimarBauer ,
I think we jst need null migration for version_name and comment

[ReimarBauer]

Where we had stored 'None' in 9.x we have to replace it by None in 10.0.0. The solution has to go into the migration script for version 10.