Yes, you're telling it to print a line by using ?

Here is some untested code to remove blank but still should do similar as Rad has already shown you.

Code:
WHILE @ERROR = 0
  $Line = Split(readline(1),",")
  If $Line
    $Line[0] + $Line[3] + $Line[19] + $Line[21] ?
  EndIf
LOOP


This would get rid of a blank but would still error if one of the elements of your array was empty
because you're telling it to use or show something that does not exist which generates the error.