What does the "!!" operator mean in Kotlin? : <p>I'm reading this <a href="https://developer.android.com/jetpack/docs/guide" rel="nofollow noreferrer">guide</a> from Google for Android and they have the snippet bellow.</p>

<p>What does the <code>!!</code> do in <code>userDao.save(response.body()!!)</code>?</p>

<pre><code>private fun refreshUser(userId: String) {
   // Runs in a background thread.
   executor.execute {
       // Check if user data was fetched recently.
       val userExists = userDao.hasUser(FRESH_TIMEOUT)
       if (!userExists) {
           // Refreshes the data.
           val response = webservice.getUser(userId).execute()

           // Check for errors here.

           // Updates the database. The LiveData object automatically
           // refreshes, so we don't need to do anything else here.
           userDao.save(response.body()!!)
       }
   }
}
</code></pre>
