title: Add List to MutableLiveData
body: <p>I have a <code>MutableLiveData</code> and I want to add a <code>List</code> inside, but seems the below code doesn't work:</p>
  
  <pre><code>    private var factsLive: MutableLiveData&lt;List&lt;Fact&gt;&gt;? = null
  
  private fun getObserver(): SingleObserver&lt;List&lt;Fact&gt;&gt; {
      return object : SingleObserver&lt;List&lt;Fact&gt;&gt; {
          override fun onSuccess(t: List&lt;Fact&gt;) {
              Log.d("test", "Succes")
              factsLive?.value = t
          }
  
          override fun onSubscribe(d: Disposable) {
              Log.d("test", "Subscribe")
          }
  
          override fun onError(e: Throwable) {
              Log.d("test", "Error")
          }
      }
  }
  </code></pre>
  
  <p>This returns me <code>MutableLiveData</code> like null.</p>