java.lang.NullPointerException at com.teamtreehouse.KaraokeMachine.promptAction(KaraokeMachine.java:27)

package com.teamtreehouse;

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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

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

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

  public KaraokeMachine(SongBook mSongBook) {
    mSongBook = mSongBook;
    mReader = new BufferedReader(new InputStreamReader(System.in));
    mMenu = new HashMap<String, String>();
    mMenu.put("add", "Add a new song to the menu");
    mMenu.put("quit", "Give up. Exit the program");
  }

  private String promptAction() throws IOException {
    System.out.printf("There are %d songs available. Your options are: %n", mSongBook.getSongCount());
    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 "quit":
          System.out.print("Thanks for playing");
          break;
          default:
          System.out.printf("Unknown choice: %s. Try again%n", choice);
        }
      }catch(IOException ioe){
        System.out.println("Problem with input");
        ioe.printStackTrace();
      } 
    }while(!choice.equals("quit"));
  }
  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 int promptFroIndex(List<String> options) throws IOException {
    int counter = 1;
    for(String option : options){
      System.out.printf("%d.) %s %n", counter, option);
      counter ++;
    }
    String optionAsString = mReader.readLine();
    int choice  = Integer.parseInt(optionAsString.trim());
    System.out.printf("Your choice %d", choice);
    return choice - 1;
  }

}

///////////////junks.java FILE STARTS HERE/////////////////////

/open model/Song.java
/open model/Songbook.java
/open KaraokeMachine.java
System.out.printf("Print this!%n");

        //MAKE A NEW MACHINE
Songbook songbook = new Songbook("BOOK ONE!");

Song song = new Song(
    "Michael Jackson",
    "Beat It",
    "https://www.youtube.com/watch?v=SaEC9i9QOvk");
System.out.printf("Adding %s %n",song);
songbook.addSong(song);
System.out.printf("There are %d songs in the book.%n", songbook.getSongCount());

KaraokeMachine machine = new KaraokeMachine(songbook);


///////////////FILE ENDS HERE/////////////////////