array formula is not working in google sheet

What I want to do:

• Check if 4 of my cells are blank or not
• If all of them are not blank, then its okay, else display nothing ("")
• I want it to be auto dragged down

What I have tried

=arrayformula(if(AND(not(A1:D=""),not(B1:B=""),not(C1:C=""),not(D1:D="")),"ok",""))

Result

• Although the statements of AND is true, it displays nothing ""

What can be the issue in the formula?