title: CakePHP: belongsTo with null value
body: <p>I have a model which has a belongsTo relation which is not required.</p>
  
  <pre><code>Banana belongsTo Basket
  banana.basket_id can be null
  </code></pre>
  
  <p>Which means that a banana can belong to a basket, but doesn't have to.</p>
  
  <p>The save operation <code>Banana-&gt;save(array('Banana' =&gt; array('basket_id' =&gt; null, 'weight' =&gt; 50)));</code> works OK, but when I read, I get this result:</p>
  
  <pre><code>array(
     'Banana' =&gt; array('id' =&gt; 10, 'basket_id' =&gt; null, 'weight' =&gt; 50),
     'Basket' =&gt; array('id' =&gt; null, 'bannana_count' =&gt; null)
  )
  </code></pre>
  
  <p>Of course, I could filter it out in afterFind, but I would rather see to have no Basket in the resulting array if basket_id is null. What to do?</p>
  
  <p>Using CakePHP 2.3.6.</p>