Exception in thread "main" java.lang.ArrayIndexOutOfBoundsExcept

import com.teamtreehouse.KaraokeMachine;
import com.teamtreehouse.model.Song;
import com.teamtreehouse.model.SongBook;

public class Karaoke {

  public static void main(String[] args) {
    SongBook songBook = new SongBook();
    songBook.importFrom("songs.txt");
    KaraokeMachine machine = new KaraokeMachine(songBook);
    machine.run();
    System.out.println("Saving book....");
    songBook.exportTo("songs.txt");
  }
}

package com.teamtreehouse.model;

import java.io.*;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.HashMap;
import java.util.Map;

public class SongBook {
  private List<Song> mSongs; 

  public SongBook() { //constructor
   mSongs = new ArrayList<Song>(); 
  }

  public void exportTo(String fileName) { 
    try (
      FileOutputStream fos = new FileOutputStream(fileName);       
      PrintWriter writer = new PrintWriter(fos);
    ) {
      for (Song song: mSongs) {
        writer.printf("%s|%s|%s%n", 
                      song.getArtist(), 
                      song.getTitle(), 
                      song.getVideoUrl());
      }
    } catch (IOException ioe) {
      System.out.printf("Problem saving %s %n", fileName);
      ioe.printStackTrace();
    }
  }

  public void importFrom(String fileName) { 
    try (
      FileInputStream fis = new FileInputStream(fileName);
      BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
    ) { 
      String line;
      while((line = reader.readLine()) != null) {
        String[] args = line.split("\\|");
        addSong(new Song(args[0], args[1], args[2])); 
      }
    } catch (IOException ioe) {
      System.out.printf("Problem loading %s %n", fileName);
    }
  }

  public void addSong(Song song) { 
    mSongs.add(song);
  }

  public int getSongCount() { 
    return mSongs.size();
  }

  //FIXME: this should be cached
  private Map<String, List<Song>> byArtist() { 
    Map<String, List<Song>> byArtist = new HashMap<>();
    for (Song song: mSongs) {
      List<Song> artistSongs = byArtist.get(song.getArtist()); 
      if (artistSongs == null) { //if the song has not been defined
        artistSongs = new ArrayList<>();
        byArtist.put(song.getArtist(), artistSongs);
      }
      artistSongs.add(song); 
    }
    return byArtist;
  }

  public Set<String> getArtists() {
    return byArtist().keySet();  
  }

  public List<Song> getSongsForArtist(String artistName) {
    return byArtist().get(artistName);  
  }
}