Type migration error when refactoring.

package com.teamtreehouse;  

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

import java.io.BufferedReader;  
import java.io.IOException;  
import java.io.InputStreamReader;  
import java.util.ArrayDeque;  
import java.util.ArrayList;  
import java.util.HashMap;  
import java.util.List;  
import java.util.Map;  
import java.util.Queue;  

public class KaraokeMachine {  
    private SongBook mSongBook;  
    private BufferedReader mReader;  
    private Map<String, String> mMenu;  
    private Queue<SongRequest> mSongRequestQueue;  

    public KaraokeMachine(SongBook songBook) {  
        mSongBook = songBook;  
        mReader = new BufferedReader(new InputStreamReader(System.in));  
        mSongRequestQueue = new ArrayDeque<>();  
        mMenu = new HashMap<String, String>();  
        mMenu.put("add", "Add a new song to the song book");  
        mMenu.put("play", "Play next song in the queue");  
        mMenu.put("choose", "Choose a song to sing!");  
        mMenu.put("quit", "Give up.  Exit the program");  
    }  

    private String promptAction() throws IOException {  
        System.out.printf("There are %d songs available and %d in the queue. Your options are:  %n",  
        mSongBook.getSongCount(),  
        mSongRequestQueue.size());  
        for (Map.Entry<String, String> option : mMenu.entrySet()) {  
            System.out.printf("%s - %s %n",  
            option.getKey(),  
            option.getValue());  
        }  
        System.out.print("What do you want to do:  ");  
        String choice = mReader.readLine();  
        return choice.trim().toLowerCase();  
    }  

    public void run() {  
        String choice = "";  
        do {  
            try {  
                choice = promptAction();  
                switch (choice) {  
                    case "add":  
                        Song song = promptNewSong();  
                        mSongBook.addSong(song);  
                        System.out.printf("%s added! %n%n", song);  
                        break; 
                    case "choose":  
                        String singerName = promptForSingerName();  
                        String artist = promptArtist();  
                        Song artistSong = promptSongForArtist(artist);  
                        SongRequest songRequest = new SongRequest(singerName, artistSong);  
                        if (mSongRequestQueue.contains(songRequest)) {  
                            System.out.printf("%n%n Whoops %s already requested %s!",  
                            singerName,  
                            artistSong);  
                            break;  
                        }  
                        mSongRequestQueue.add(songRequest);  
                        System.out.printf("You chose: %s %n", artistSong);  
                        break;
                    case "play":  
                        playNext();  
                        break;
                    case "quit":  
                        System.out.println("Thanks for playing!");  
                        break;
                    default:  
                        System.out.printf("Unknown choice:  '%s'. Try again. %n%n%n",  
                        choice);  
                }  
            } catch (IOException ioe) {  
                System.out.println("Problem with input");  
                ioe.printStackTrace();  
            }  
        } while (!choice.equals("quit"));  
    }  

    private String promptForSingerName() throws IOException {  
        System.out.print("Enter the singer's name:  ");  
        return mReader.readLine();  
    }  

    private Song promptNewSong() throws IOException {  
        System.out.print("Enter the artist's name:  ");  
        String artist = mReader.readLine();  
        System.out.print("Enter the Title: ");  
        String title = mReader.readLine();  
        System.out.print("Enter the video URL:  ");  
        String videoUrl = mReader.readLine();  
        return new Song(artist, title, videoUrl);  
    }  

    private String promptArtist() throws IOException {  
        System.out.println("Available artists:");  
        List<String> artists = new ArrayList<>(mSongBook.getArtists());  
        int index = promptForIndex(artists);  
        return artists.get(index);  
    }  

    private Song promptSongForArtist(String artist) throws IOException {  
        List<Song> songs = mSongBook.getSongsForArtist(artist);  
        List<String> songTitles = new ArrayList<>();  
        for (Song song : songs) {  
            songTitles.add(song.getTitle());  
        }  
        System.out.printf("Available songs for %s: %n", artist);  
        int index = promptForIndex(songTitles);  
        return songs.get(index);  
    }  

    private int promptForIndex(List<String> options) throws IOException {  
        int counter = 1;  
        for (String option : options) {  
            System.out.printf("%d.)  %s %n", counter, option);  
            counter++;  
        }  
        System.out.print("Your choice:  ");  
        String optionAsString = mReader.readLine();  
        int choice = Integer.parseInt(optionAsString.trim());  

        return choice - 1;  
    }  

    public void playNext() {  
        SongRequest songRequest = mSongRequestQueue.poll();  
        if (songRequest == null) {  
            System.out.println("Sorry there are no songs in the Queue." +  
            "Use choose from the menu to add some");  
        } else {  
            Song song = songRequest.getSong();  
            System.out.printf("%n%n%n Ready %s? Open %s by %s to hear %s %n%n%n",  
            songRequest.getSingerName(),  
            song.getVideoUrl(),  
            song.getArtist(),  
            song.getTitle());  
        }  
    }  
}