Adding feed freezes - image field wrong type in table aggregator_feed

I could not add a feed since the browser just froze. I tracked it down to the database table "aggregator_feed". Here, it couldn't insert an entry if image was not given. The setting for field "image" seems to be conflicting. On the one hand it is checked "Not Null". On the other hand no default value can be given for type "blob/text". This might be a mysql thing.
I fixed it by removing the "Not Null" criteria.

If anyone else has the same problem, this might be the place to fix in feedmanager.install: