title: Laravel string validation to allow empty strings
body: <p>In Laravel 5.7 I am using form request validation:</p>
  
  <pre><code>public function rules() 
  {
      return [
          'age' =&gt; 'integer',
          'title' =&gt; 'string|max:50'
      ];
  }
  </code></pre>
  
  <p>If I submit a request to my API with this payload:</p>
  
  <pre><code>{
    "age": 24,
    "title": ""
  }
  </code></pre>
  
  <p>Laravel returns the error:</p>
  
  <pre><code>{
      "message": "The given data was invalid.",
      "errors": {
          "title": [
              "The title must be a string."
          ]
      }
  }
  </code></pre>
  
  <p>I would expect it to pass the validation, since the title is a string, albeit an empty one. How should the validation be formulated to allow empty strings?</p>