title: Firestore how to combine orderBy desc with startAfter(null)
body: <p>I've been searching for this one for a while but have not found a reason why this is the way it is.</p>
  
  <p>Basically this returns an array of documents in the collection.</p>
  
  <pre><code>this.db.collection('people', ref =&gt; {
      return ref.orderBy(name, 'asc')
                .startAfter(null)
                .limit(10)
  })...
  </code></pre>
  
  <p>This returns an empty array.</p>
  
  <pre><code>this.db.collection('people', ref =&gt; {
      return ref.orderBy(name, 'desc')
                .startAfter(null)
                .limit(10)
  })...
  </code></pre>
  
  <p>The only difference is orderBy is set to 'desc'.  Can someone please explain why this happens and a way around it?  Thanks in advance!</p>