title: CakePHP integer field default null failing validation on save() after read() or create()
body: <p><strong>Schema:</strong></p>
  
  <pre><code>vacation_request_denial_reason_id int(11) DEFAULT NULL,
  </code></pre>
  
  <p><strong>Model:</strong></p>
  
  <pre><code>class VacationRequest extends AppModel {
      var $name = 'VacationRequest';
      var $actsAs = array('Containable');
      var $validate = array('employee_id' =&gt; array('numeric' =&gt; array('rule' =&gt; array('numeric'))),
          'approving_supervisor_id' =&gt; array('numeric' =&gt; array('rule' =&gt; array('numeric'))),
          'vacation_request_status_id' =&gt; array('numeric' =&gt; array('rule' =&gt; array('numeric'))),
          'vacation_hours' =&gt; array('numeric' =&gt; array('rule' =&gt; array('numeric'))),
          'vacation_request_denial_reason_id' =&gt; array('numeric' =&gt; array('rule' =&gt; array('numeric'))));
  </code></pre>
  
  <p><strong>Controller:</strong></p>
  
  <pre><code>function add() {
    if (!empty($this-&gt;data)) {
      $this-&gt;VacationRequest-&gt;create();
      if ($this-&gt;VacationRequest-&gt;save($this-&gt;data)) {
        // ...
      }
    }
  }
  </code></pre>
  
  <p>This code fails validation for <code>vacation_request_denial_reason_id</code>...</p>
  
  <p>I've narrowed the problem down to whenever I attempt to call <code>Model-&gt;save()</code> after calling either a <code>Model-&gt;read()</code> or <code>Model-&gt;create()</code>. Proven by the fact the code will work if I comment out the <code>create()</code> call.</p>
  
  <p>I dare call this a bug. However, I feel like I've experienced this before for integer columns specifically and forgot the work around. Any guidance is appreciated.</p>
  
  <h3>UPDATE</h3>
  
  <p>I should note that <code>vacation_request_denial_reason_id</code> is not part of <code>$this-&gt;data</code> in the form submission. So it's definitely odd that it's failing validation. Furthermore, it is not my intention to use <code>'allowEmpty' =&gt; true</code> in the validation rule. When it is present in <code>$this-&gt;data</code>, I want to ensure it is numeric.</p>