title: Recommendation for LONGTEXT empty value: '' or NULL
body: <p>I have a field called <code>synopsis</code> -- sometimes this will be provided and sometimes it won't. Is there any difference in storing the default value as an empty string with the field being <code>NOT NULL</code> vs. storing the value as <code>NULL</code>?</p>
  
  <p>The two comparative fields would be:</p>
  
  <pre><code>- `synopsis` longtext NOT NULL DEFAULT ''
  - `synopsis` longtext NULL DEFAULT NULL
  </code></pre>
  
  <p>What is recommended here? Why?</p>