title: LiveData does not emit required value
body: <p>I have my live data created like this:</p>
  
  <pre><code>val authTokenLiveData: LiveData&lt;String?&gt; = liveData {
      emit(accountManager.myAuthToken())
  }
  </code></pre>
  
  <p>And I am observing it like it:</p>
  
  <pre><code>accountViewModel.authTokenLiveData.observe(this) {
      toast("Token is $it")
      if(it == null) goToLogin()
  }
  </code></pre>
  
  <p>It works well at first, I get the token toasted, however when I logout, and hence remove the token such that the token is <code>null</code>, I do not go to login which I should according to my observer.</p>
  
  <p>How do I ensure that the <code>authTokenLiveData</code> emits <code>null</code> when the token becomes <code>null</code> so that my observer allows me to go to the login screen?</p>