title: Convert left join query to Yii2 db active record
body: <p>I have the following query:</p>
  <p><code>SELECT karyawan.* FROM karyawan LEFT JOIN user ON user.id_karyawan = karyawan.id WHERE user.id_karyawan IS NULL</code></p>
  <p>and I use db active record like this:</p>
  <pre class="lang-php prettyprint-override"><code>$query = Karyawan::find()
      -&gt;select('*')
      -&gt;leftJoin('user', 'user.id_karyawan = karyawan.id')
      -&gt;where(['is', 'karyawan.id', new \yii\db\Expression('null')])
      -&gt;with('user')
      -&gt;all();
  </code></pre>
  <p>But it doesn't work. What's wrong with my db active record?</p>