title: cakePHP value for empty option
body: <p>is there a way to pass a value for the empty option in a select dropdown generated by the FormHelper?</p>
  
  <p>I'm creating an input like this:</p>
  
  <p><code>echo $this-&gt;Form-&gt;input('supplier_id', array('empty'=&gt;true));</code></p>
  
  <p>with values supplied automatically from the controller like this</p>
  
  <pre><code>$suppliers = $this-&gt;Product-&gt;Supplier-&gt;find('list');
  $this-&gt;set(compact('suppliers'));
  </code></pre>
  
  <p>and the select box is created like this:</p>
  
  <pre><code>&lt;select name="data[Product][supplier_id]" class="form-control" id="ProductSupplierId"&gt;
    &lt;option value=""&gt;&lt;/option&gt;
    &lt;option value="1"&gt;Lolë Montreal&lt;/option&gt;
    &lt;option value="2"&gt;Spiritual Gangster&lt;/option&gt;
    &lt;option value="3"&gt;Havaianas&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>but I would like the first option (the empty one) to have a value of 0 instead of '' is it possible? or should I instead modify the <code>$suppliers</code> array in the controller with something like </p>
  
  <pre><code>$suppliers[0] = '';
  </code></pre>
  
  <p>and remove the empty option from the FormHelper input?</p>