Using ZenCart v1.3.9e on Windows Server with MySQL 5.1.44-community server.

While using the ACP Banner Manager, when I enter a blank expiry date and blank expiry impressions number, I'm being given the following:

1292 Incorrect datetime value: 'null'
in:
[UPDATE zen_banners SET date_scheduled = '20100801', expires_date = DATE_ADD('null', INTERVAL '23:59:59' HOUR_SECOND), expires_impressions = null WHERE banners_id = 9]
If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.

The only suggestion that I have is to remove any 'NULL' or 'null' values and simply assign a value of '' instead. MySQL will automatically note that the 0 length string is NULL and assign it as such. The same holds true if ALL schedule values is blank.