title: Laravel 5.3 Validation Fails when Variables are Null
body: <p>Since upgrading laravel from 5.1 to 5.3, I've got couple of odd issues with Validation.</p>
  
  <p>When I post a data like this:</p>
  
  <pre><code>firstName    null
  </code></pre>
  
  <p>And the validation rules are like this:</p>
  
  <pre><code>$validator = Validator::make($postData, [
                'firstName'           =&gt; 'string|max:255',
                'lastName'            =&gt; 'string|max:255'
              ]);
  </code></pre>
  
  <p>The above fails with the messages something like <code>"The XYZ must be a string."</code>. What I don't understand is:</p>
  
  <ol>
  <li><p>Why is the validation failing when it is not set as <code>required</code>?
  Meaning, it should ignore it and not throw an error if the value is
  empty, right?</p></li>
  <li><p>Why does the validation fail if the value is set as <code>null</code>?</p></li>
  <li><p>Why does the validation fail when the parameter is not sent at all?
  (like the <code>lastName</code> which is not posted at all)</p></li>
  </ol>
  
  <p>Has something changed in Laravel 5.3 validations?</p>