title: DataSnapshot is missing a constructor with no arguments
body: <p>I am implementing Firebase Recyclerview UI in my application. I have implemented a recyclerview adapter and it shows me following exception. 
  Following is my adapter code : </p>
  
  <pre><code>FirebaseRecyclerAdapter&lt;DataSnapshot, MyHolder&gt; recyclerAdapter = new FirebaseRecyclerAdapter&lt;DataSnapshot, MyHolder&gt;(
                  DataSnapshot.class,
                  R.layout.row_slots,
                  MyHolder.class,
                  databaseReference.child("slots").child(uid).child(dayOfWeek).child("time")
          ) {
              @Override
              protected void populateViewHolder(MyHolder viewHolder, DataSnapshot model, int position) {
  
                  System.out.println("Key : "+model.getKey());
  
              }
  
          };
  </code></pre>
  
  <p>It is showing following exception : 
  <a href="https://i.stack.imgur.com/stn0C.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/stn0C.png" alt="enter image description here"></a></p>
  
  <p>How can I get a snapshot value using FirebaseRecyclerAdapter?</p>