title: Symbol's value as variable is void: dired-mode-map
body: <p>I'm trying to remap some keys in dired like this:</p>
  
  <pre><code>(add-hook 'dired-mode-hook
    (lambda ()
      (require 'dired )
      (define-key dired-mode-map (kbd "M-o") nil)))
      (define-key dired-mode-map (kbd "M-o") 'other-window)
      ))
  </code></pre>
  
  <p>Unfortunately this doesn't seem to work, I get this error</p>
  
  <pre><code>Symbol's value as variable is void: dired-mode-map
  </code></pre>
  
  <p>Which is werid, because I should be loading in dired. What could I be doing wrong?</p>