Ruby：没有救援的其他方面毫无用处

我是ruby的新手.我正在尝试编写一个apache error.log监视器.它主要完成了,但我收到了警告：否则没有救援就没用了.
我无法弄清楚我做错了什么. Ruby要我使用’除非’吗？

class ErrorMonitor
   @@previous_size=0
   @@counter=0

   def initialize()
   end

   def process
    if @@counter > 0
       @new_size= File.stat('/var/log/apache2/error.log').size
       if @new_size > @@previous_size
          for i in @@previous_size..@new_size - @@previous_size
             print IO.readlines("/var/log/apache2/error.log")[i]
          end
          @@previous_size = @new_size
       end
    end
    else
       @@previous_size= File.stat('/var/log/apache2/error.log').size
       @@counter=1;
    end # <- this line is where the warning points to
   end


# main execution
em = ErrorMonitor.new()
while true
    em.process
    sleep 10
end

解决方法

if condition
  # …
else
  # …
end

不

if condition
  # …
end
else
  # …
end