title: CakePHP how to submit NULL value?
body: <p>On web form I have select-option field. It have to submit value 'card' (without quotes), or NULL value.</p>
  
  <p>Now, code looks like this:</p>
  
  <pre><code>    $options = array(NULL =&gt; 'Invoice', 'card' =&gt; 'Payment card');
      echo $this-&gt;Form-&gt;input('payment_method', array('options'=&gt;$options));
  </code></pre>
  
  <p>How can I define options array, to submit NULL value in database table (and/or 'card', but that works of course), in case that Invoice option is selected?</p>
  
  <p>Thank you in advance!</p>