Emptying protolog URI does not work
The protolog URI field can not be fully emptied but only deleted.
If you empty the protolog field and save this no error is returned but when refereshing or reloading the data the old URI is still there.
Empty URIs might not be wanted, but this needs to be handled either by an exception/warning or by fully removing the according record.
The current behavior is unexpected.
I found this when reviewing #5948