Fix that ConcurrentModificationException at last!
Return empty string if Player has no IP address.
implodeArray and implodeKeyValueArray should take Objects and toString them.
Add getColumnNames() to Database, reorganize code in it and its subclasses.
Specify value for last_active column when creating account.
Replace existing code which adds missing last_active column with detection and addition of missing columns, remove NOT NULL from all column types.