title: BoundaryCallback for PagedList never gets called
body: <p>I've created a Room Database on my device, which returns </p>
  
  <pre><code>// The Int type parameter tells Room to use a PositionalDataSource object.
  @Query("SELECT * FROM Word ORDER BY id")
  abstract fun getByFactory(): DataSource.Factory&lt;Int, Word&gt;
  </code></pre>
  
  <p>This factory call is then used in my repository, where I connect it with my boundaryCallback</p>
  
  <pre><code>val boundaryCallback = MyBoundaryCallback()
  return wordDao.getByFactory().toLiveData(
     pageSize = 20,
     boundaryCallback = boundaryCallback
  )
  </code></pre>
  
  <p>My boundary callback is basic and looks like that</p>
  
  <pre><code>class MyBoundaryCallback() : PagedList.BoundaryCallback&lt;Word&gt;() {
  
      val int = 0;
  
      @MainThread
      override fun onItemAtFrontLoaded(itemAtFront: Word) {
          Timber.d("hello")
      }
  
      @MainThread
      override fun onZeroItemsLoaded() {
          Timber.d("hello")
      }
  
      @MainThread
      override fun onItemAtEndLoaded(itemAtEnd: Word) {
          Timber.d("hello")
      }
  }
  </code></pre>
  
  <p>The problem is that, although my datasource (room database) doesn't contain any entries, the boundary callbacks don't get called.
  Do you have any clues what could be the problem?</p>