title: Inserting null values with liquibase
body: <p>We use liquibase to manage one of our MySQL databases' updates, rollbacks, etc.</p>
  
  <p>One small curiosity I've come across is the process of setting values to null in the course of updates or rollbacks. Example:</p>
  
  <pre><code>        &lt;rollback&gt;
              &lt;update tableName="boats"&gt;
                  &lt;column name="engine" value="null" /&gt;
                  &lt;column name="oars" value="2" /&gt;
  </code></pre>
  
  <p>At first I was a bit worried that "null" would literally insert the string "null", but it turns out that liquibase seems to have some smarts that actually inserts a null value.</p>
  
  <p>I was wondering if this was the recommended way of doing this, or whether there is a platform-agnostic way of saying 'nullValue' explicitly within Liquibase?</p>