title: Error in flutter: Document references must have an even number of segments
body: <p>I have a collection named <code>memssages</code> and have to find document where field <code>begin</code> is equal to false. Code is like below.</p>
  
  <pre><code>Future&lt;String&gt; getRoomID() async {
    QuerySnapshot snapshot = await sl.get&lt;FirebaseAPI&gt;().getFirestore()
      .collection('messages')
      .where('begin',isEqualTo: false).getDocuments();
    if(snapshot.documents.length==0){
      return '';
    } else {
      Random random = Random();
      DocumentSnapshot document = snapshot.documents[random.nextInt(snapshot.documents.length)];
      return document.documentID;
    }
  }  
  </code></pre>
  
  <p>But It occurs fatal error like my post title.</p>
  
  <blockquote>
    <p>java.lang.IllegalArgumentException: Invalid document reference.
    Document references must have an even number of segments, but messages
    has 1</p>
  </blockquote>
  
  <p>What is wrong with me? I was suffered whole day...</p>
  
  <p><a href="https://i.stack.imgur.com/ZEWkc.png" rel="nofollow noreferrer">Database ScreenShot</a></p>