idk why do u think that it's Advanced kick or kb.

;1. u don't must to Check ($2- != $null) u can use $$2 -
 on *:text:!adkb *:#privatechannel: {
    mode $$2 +b $$3
    kick $$2 $$3 $4-
}

;2.u can use

on @*:TEXT:!k*:#:{
  if ($nick == user) {  kick $$2 $$3 $4 }
}
;or 
on @*:TEXT:!k *:#:{
  if ($nick == user) {  kick  $chan $$2 $3- }
}

simpely