AFFECTS ONLY v1.5.5c and v1.5.5d :

Symptom: SQL error: Incorrect datetime value: 'null' when editing products in the Admin.

Solution:
The quickest fix is to revert the /admin/includes/functions/database.php file to what was in v155b, by changing the 2 uppercase 'NULL' back to lowercase 'null' in the zen_db_perform() function, on lines 26 and 42:

Code:
          case 'NULL':
becomes
Code:
          case 'null':
https://github.com/zencart/zencart/c...ee18989eadd481

https://www.zen-cart.com/showthread....49#post1323749


NOTE: IN FUTURE VERSIONS IT WILL BE CHANGED BACK TO UPPERCASE 'NULL'. So if you're using something newer than v1.5.5d, THE ABOVE "fix" DOES NOT APPLY TO YOU