Hello,

If your dropdown has empty field and you set it required, then you should see this prompt:
http://prntscr.com/gtfo8r

Code i have used here:

$col = array();
$col["title"] = "Client";
$col["name"] = "client_id";
…
$col["edittype"] = "select"; // render as select
$str = $g->get_dropdown_values("select distinct client_id as k, name as v from clients");

$col["editoptions"] = array("value"=>":;".$str); // <——————————— empty option here at start
$col["editrules"] = array("required"=>true); // <——————————— required to true
$col["formatter"] = "select"; // display label, not value
$cols[] = $col;

I actually figured it out. I added this:

$col["editoptions"] = array("value"=>":;".$str);