title: Error: Call to a member function addDays() on string
body: <p>I want to add days on specified date. This is my code:</p>
  
  <pre><code>if (Carbon::now() &lt;= $campaign-&gt;s_lastrun-&gt;addDays(28)) {
         $onAir = 1;
  }
  </code></pre>
  
  <p>It worked until I made some changes on my database, and now I am getting an error: <code>Call to a member function addDays() on string</code> even though <code>s_lastrun</code> has column type <code>DATE</code>.
  Any ideas?</p>