title: Is better use an empty value as a '' or as NULL?
body: <p><strong>Database schema</strong></p>
  
  <p>I have this fields:</p>
  
  <ul>
  <li>title (string)</li>
  <li>subtitle</li>
  <li>description (string)</li>
  </ul>
  
  <p>Is better set the default value as an <strong>empty string ''</strong> or a <strong>NULL</strong>?</p>
  
  <p>For better reading/writing and size-storage performance</p>