title: NoMethodError: undefined method `+@' for "some sting":String
body: <p>My rails app just started receiving this error today. Here is the code context. It is throwing the error on the line that starts with <code>new_host_id</code></p>
  
  <pre><code>while @host_ids.include?(new_host_id)
    i++
    new_host_id = duplicate_host_id + i.to_s
  end
  </code></pre>