Have you got a script example?

I was doing if (! isNull _item) where item was an object. I tested to be sure it was not null but my script never executed after that line. using a hit isNull _item displayed false, but the script didn't execute past the if statement, by changeing it to:

_value = isNull _item;
if (!_value)

it worked that way.

if (!isNull objNull) then {hint "not null"} else {hint "null"}

hint shows "null" as it should

Please provide a full example of your script where we can actually see what <i>_item</i> is.

Unable to reproduce, no reaction on feedback request for a long time. Closing as no bug.