title: Firebase returning data that does not exist. How can I fix it?
body: <p>I have three objects (Book, Listicle_modell and Feed_modell) and I want to retrieve in a list of objects. 
  But I'm obtaining data from Firebase Database that does not exist.</p>
  
  <p>My firebase structure:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>-userid 
   - key
     -name2: Nova Conta
     -title: The best music in the world;
     -thumbnail: url;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://i.stack.imgur.com/EZ9md.png" rel="nofollow noreferrer">enter image description here</a>**i just have one child, why I'm getting Firebase give me three objects ? **.</p>
  
  <p>In my Database I just have one child that has values that matchs Feed_modell, but I'm getting the layout from book and listicles either without having these objects (keys that match book.class and listicle) in my database as the pics show:
  <a href="https://i.stack.imgur.com/fKlQf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fKlQf.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/gCdtM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gCdtM.png" alt="enter image description here"></a></p>
  
  <p>The problem is this: ** these two images that have no title, no thumbnail, no name, just have a views written, are being <strong>called</strong> but they do <strong>not exist</strong>, <em>the Test Ad is working perfectly</em>.</p>
  
  <p>This is my Android code:</p>
  
  <pre><code>    dbforFeed = FirebaseDatabase.getInstance().getReference("feedPosts").child(feedReceivingKey);
  
      dbforFeed.addChildEventListener(new ChildEventListener() {
          @Override
          public void onChildAdded(DataSnapshot dataSnapshot, String s) {
  
              Feed_modell post = dataSnapshot.getValue(Feed_modell.class);
              Book book = dataSnapshot.getValue(Book.class);
              Listicle_modell lm = dataSnapshot.getValue(Listicle_modell.class);
  
              feedList.addAll(Arrays.asList(post, book, new all_modell("ca-app-pub-4452407171570296~9731286762"), lm));
  
              recyclerViewFeedAdapter.notifyDataSetChanged();
          }
  
          @Override
          public void onChildChanged( DataSnapshot dataSnapshot, String s) {
  
          }
  
          @Override
          public void onChildRemoved( DataSnapshot dataSnapshot) {
  
          }
  
          @Override
          public void onChildMoved( DataSnapshot dataSnapshot, String s) {
  
          }
  
          @Override
          public void onCancelled( DatabaseError databaseError) {
  
          }
      });
  </code></pre>
  
  <p>Here is my database structure</p>
  
  <p><a href="https://i.stack.imgur.com/QSbUw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QSbUw.png" alt="enter image description here"></a></p>