Program i made for a friend to manage his programs and such, thought id post it here :P. just one question that i cant figure out, I need to figure out how to add error checking, like making the script halt if they try to click run and nothing is selected. would if be like

if($did(1).seltext == $null) { halt } 
else {

}

if any one could answer this for me it be greatly appreciated.
-HH

;;;;;;;;;;;;;;;;;;;
;;Program Manager;;
;;HeatedHeart----;;
;;;;;;;;;;;;;;;;;;;
;### Popups
menu status,channel,menu {
  Program Manager:dialog -vmd ProgMan ProgMan
}
;### Alias
alias refresh {
  did -r $dname 1
  var %x $hget(ProgMan,0).item
  var %Loop 1
  while (%Loop <= %x) {
    did -a $dname 1 $Hget(ProgMan, %loop).item
    inc %loop
  }
}
Alias Prog# {
  var %x $hget(ProgMan,0).item
  did -r $dname 8
  did -a $dname 8 %x
}
;### Dialog
dialog ProgMan {
  title "Program Manager"
  size -1 -1 275 261
  option pixels notheme
  list 1, 1 5 194 263
  box "", 2, 194 0 82 147
  button "Add", 3, 197 8 75 25
  button "Remove", 4, 198 34 74 25
  button "Clear", 5, 199 118 73 25
  button "Run", 6, 199 62 73 25
  button "Run as Parent", 7, 199 90 73 25
  text "", 8, 242 242 30 17
}
;### Startup
on *:LOAD:{ 
  hmake ProgMan 10
}
on *:START:{ 
  hmake ProgMan 10
  hload ProgMan ProgMan.txt
}
on *:DIALOG:ProgMan:close:*: {
  hsave ProgMan ProgMan.txt
}
on *:EXIT:{ 
  hsave ProgMan ProgMan.txt
}
on *:DIALOG:ProgMan:init:*: {
  Refresh
  prog#
}
;### Coding
on *:dialog:ProgMan:dCLICK:*: {
  if ($did == 1) {
    run $qt($Hget(ProgMan,$did(1).seltext))
  }
}
on *:dialog:ProgMan:sCLICK:*: {
  if ($did == 3) {
    var %x $sfile(dir)
    hadd ProgMan $Gettok(%x,$numtok(%x,92),92) %x
    refresh
    prog#
  }
  if ($did == 5) {
    hfree ProgMan
    hmake ProgMan 10
    did -r $dname 1
    refresh
    prog#
  }
}
on *:dialog:ProgMan:sCLICK:*: {
  if ($did == 4) {
    hdel ProgMan $did(1).seltext
    refresh
    prog#
  }
  if ($did == 6) {
    run $qt($Hget(ProgMan,$did(1).seltext))
  }
  if ($did == 7) {
    var %x $sfile(dir)
    run $qt($Hget(ProgMan,$did(1).seltext)) $qt(%x)
    unset %Ready
  }
}