Problem when condition with lookup field in Zoho Creator

Problem when condition with lookup field in Zoho Creator

this is my code:
  1. if input.promotions1 != null
  2. {
  3. info input.promotions1;
  4. }
And this my result:

when i info input.promotion1 (which is a lookup field), it turn back nothing, so what type of this field is?
normally i use the condition: if lookup_field == null then do something, but now, it's obviously null but it doesn't do anything
when i script it like: if lookup_field != null  then info lookup_field and it turns out to be nothing there.

there is a bug or something?