can you tell me what is the proper syntax to filter for no PO number in the PO field in the filter area in reports? i figure if i know what it is for 'blank' then i can negate that to get 'not blank'.

i know it is capable of comparative search because if i try to search for a specific PO number it does find it. also, if i search with just a part of a PO number it gives me all estimates with POs that contain that part, i.g. if i have 47 in the PO field, the results are 3591470, 3572447, A1547521. so the functionality is there.

i just dont know the proper syntax for 'something/anything in PO field' or 'nothing in PO field'? 

if you dont know, can you put me in touch with someone who would know?