not possible to have non-expiring contracts

When creating a new role contract, the documentation for the "Days until Expiry" field says "Leave blank for no Expiration", but this actually seems not to be true. When entering nothing, the value is treated as 0 and leads to a valid expiration date, namely the next day. After all, the column "end" is NOT NULL, so it's actually not possible to have a contract that does not expire.

To overcome this, one would have to drop the NOT NULL constraint on the end column and insert a value there only if $expire>0.