title: How to set a multidimentional array in session with rails
body: <p>I am trying to do something like this : </p>
  
  <pre><code>session[:continent][:filter] = params[:filter]
  </code></pre>
  
  <p>but it doesn't work, i got this error :</p>
  
  <pre><code>You have a nil object when you didn't expect it!
  You might have expected an instance of Array.
  The error occurred while evaluating nil.[]=
  </code></pre>