code: public String getAttribute(String key)
      {
          return (String) attributes.get(key.toLowerCase(Locale.ENGLISH));
      }
docs: Returns the value of the attribute with the given key.
  <p>
  This is particulary important when a response contains special attributes
  that are dependent on the action that has been sent.
  <p>
  An example of this is the response to the GetVarAction. It contains the
  value of the channel variable as an attribute stored under the key of the
  variable name.
  <p>
  Example:
  
  <pre>
  GetVarAction action = new GetVarAction();
  action.setChannel("SIP/1310-22c3");
  action.setVariable("ALERT_INFO");
  ManagerResponse response = connection.sendAction(action);
  String alertInfo = response.getAttribute("ALERT_INFO");
  </pre>
  
  As all attributes are internally stored in lower case the key is
  automatically converted to lower case before lookup.
  
  @param key the key to lookup.
  @return the value of the attribute stored under this key or
  <code>null</code> if there is no such attribute.