title: com.google.firebase.database.DatabaseException
body: <p>When I start the activity, it is showing the error:</p>
  
  <blockquote>
    <p>Class com.rcpl.agni.Artist does not define a no-argument
    constructor.If you are using ProGuard, make sure these constructors
    are not stripped.</p>
  </blockquote>
  
  <pre><code>protected void onStart() {
          super.onStart();
          ref.addValueEventListener(new ValueEventListener() {
              @Override
              public void onDataChange(DataSnapshot dataSnapshot) {
                  //artistList.clear();
                  for(DataSnapshot artistSnapshot : dataSnapshot.getChildren()){
                      Artist artist = artistSnapshot.getValue(Artist.class);
                      Toast.makeText(MainActivity.this, artist.getArtistName(), Toast.LENGTH_SHORT).show();
  
                  }
  
              }
  
              @Override
              public void onCancelled(DatabaseError databaseError) {
  
              }
          });
      }
  </code></pre>
  
  <p>Artist.java</p>
  
  <pre><code>package com.rcpl.agni;
  
  /**
   * Created by Dell-pc on 23-01-2018.
   */
  
  public class Artist {
      String artistId;
      String artistName;
      String artistGenre;
  
      public Artist(String artistId, String artistName, String artistGenre) {
          this.artistId = artistId;
          this.artistName = artistName;
          this.artistGenre = artistGenre;
      }
  
      public String getArtistId() {
          return artistId;
      }
  
      public String getArtistName() {
          return artistName;
      }
  
      public String getArtistGenre() {
          return artistGenre;
      }
  }
  </code></pre>