title: Document references must have an even number of segments error on a collection reference
body: <p>I'm getting the rather simple error: </p>
  
  <pre><code>Document references must have an even number of segments.
  </code></pre>
  
  <p>I'm aware of what it is telling me and how to fix it, however it is giving me this error on a collection reference.</p>
  
  <pre><code>CollectionReference collectionReference = getFirebaseInstance()
  .collection(Constants.USERS)
  .document(userId)
  .collection(Constants.CONTACTS);
  </code></pre>
  
  <p>In my database the path is (COLLECTION) &lt; DOCUMENTS > (COLLECTION) &lt; DOCUMENTS > I'm trying to get all contacts for a user at users/{id}/contacts but it just throws this error, any ideas?</p>
  
  <p>getFirebaseInstance is a method I've created to always get the current </p>
  
  <pre><code>FirebaseFirestore.getInstance();
  </code></pre>