Empty value stored as NULL in Autocomplete
This is by design since version 7.2.6 (Oct 2017). The empty value is stored as SQL null. If you must change, update in set_col_edittype() method in cls_datagrid.php.
Require source code - commercial licenses only:
In the last line of set_col_edittype(),
$keyvalue_pair = ($required ? '' : 'null') .":;".$select_list;
Change it to:
$keyvalue_pair = ":;".$select_list;