title: Validation: how to set a field that is not required to 'null' when input is empty
body: <p>I have a validation rule that looks like this:</p>
  
  <pre><code>$rules = ['target' =&gt; 'numeric'];
  </code></pre>
  
  <p>It's not a required field. If a value is not specified in the input (i.e. Input::get('target') == ''), I want the field to be set to NULL in the database.</p>
  
  <p>Currently the above rule passes, and in the absence of a numeric input, it gets set to 0 in the database.</p>
  
  <p>What's the best solution?</p>