BUG: empty fields return the string "undefined" when checked on ajax events

Checking for a integer key field named “id_prj” on a form app.

On a (not yet inserted) new record on the onLoad event, this code:

$m = empty({id_prj}) 
		? "empty id" 
		: "id_prj = '" . {id_prj} . "'";
echo $m;
sc_alert($m);

will show, correctly, this:

empty id


But if the same code is run from an an Ajax event of one of the form fields, still on a not inserted new record, it will show:

id_prj = ‘undefined’

I.e. the empty integer field has the string “undefined” as its value.
Why?

Not sure, but i think this was not the case in past SC versions (no idea when this behavior was introduced).

This is definitely a dangerous bug for all code run on ajax events of form fields.