tell application "iTunes"
  set thePlaylist to library playlist 1
  set musicFiles to the file tracks of thePlaylist

  repeat with mf in musicFiles
    --the name of mf as string
    set hasLoc to ""
    if (the location of mf as string ¬
     is equal to "missing value") then
      try
        set comment of mf to the comment of mf & ""
      end try
    end if
  end repeat
end