title: Firebase's orderBychild().equals is not fetching any data
body: <p>Consider:</p>
  
  <pre><code>mDatabase = FirebaseDatabase.getInstance().getReference("archive");
  mDatabase.orderByChild("_age").equalTo("20").addValueEventListener(new ValueEventListener() {
      @Override
      public void onDataChange(DataSnapshot dataSnapshot) {
          value = dataSnapshot.getValue(String.class);
          tSResult.setText(value);
      }
  
      @Override
      public void onCancelled(DatabaseError error) {
  
          Log.w(TAG, "Failed to read value.", error.toException());
      }
  });
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/bOUx2.png" rel="nofollow noreferrer">Firebase Database</a>.</p>
  
  <p><code>tSResult</code> is a TextView I'm using just to test the returned data.</p>
  
  <p>I'm trying to run this code, but my application either crashes or does not return any result.</p>
  
  <p>Log:</p>
  
  <blockquote>
    <p>04-26 19:51:24.146 4372-4372/com.example.joe.orside E/AndroidRuntime: <br/>
    FATAL EXCEPTION: main <br/>
      Process: com.example.joe.orside, PID: 4372 <br/>
      com.google.firebase.database.DatabaseException: Failed to convert <br/>
    value of type java.util.HashMap to String <br/>
      at com.google.android.gms.internal.zzbqi.zzaD(Unknown Source) <br/>
      at com.google.android.gms.internal.zzbqi.zzb(Unknown Source) <br/>
      at com.google.android.gms.internal.zzbqi.zza(Unknown Source) <br/>
      at com.google.firebase.database.DataSnapshot.getValue(Unknown Source) <br/>
      at <br/>
    com.example.joe.orside.MainActivity$8$1.onDataChange(MainActivity.java:755) <br/>
      at com.google.firebase.database.Query$1.onDataChange(Unknown Source) <br/>
      at com.google.android.gms.internal.zzbmz.zza(Unknown Source) <br/>
      at com.google.android.gms.internal.zzbnz.zzYj(Unknown Source) <br/>
      at com.google.android.gms.internal.zzboc$1.run(Unknown Source) <br/>
      at android.os.Handler.handleCallback(Handler.java:751) <br/>
      at android.os.Handler.dispatchMessage(Handler.java:95) <br/>
      at android.os.Looper.loop(Looper.java:154) <br/>
      at android.app.ActivityThread.main(ActivityThread.java:6119) <br/>
      at java.lang.reflect.Method.invoke(Native Method) <br/>
      at <br/>
    com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) <br/>
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) <br/></p>
  </blockquote>
  
  <p>Any suggestions?</p>