Checking for a comment in an event

[Itachi62]

Alright, scripting newb here.
I'm trying to create a simple script which will call a common event if a comment is there, first I got no errors but it didn't work, now it is getting errors and doesn't work at all.

class Comment_Stuff
  
event = $game_map.events[event_id]
  unless event.erased
    unless event.list.nil?
      event.list.each do |event_command|
        if event_command.code == 108 && event_command.code == 408
          string = event_command.paramters[0]
            if string.include?('Test')
              # Launch the common event
            $game_temp.common_event_id = 8
          end
        end
      end
    end
  end
end

The error is on line 3, and it says "undefined method 'events' for nil:NilClass"
I have no idea what this means, and I can't figure out what to do.

Can somebody help me with this simple script?
Please say it easy enough for a newb to understand. @_@
Thanks.