error: can't retrieve from static content

package com.teamtreehouse;

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

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


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

  public KaraokeMachine(SongBook songBook) {
    mSongBook = songBook;
    mReader = new BufferedReader(new InputStreamReader(System.in));
    mSongQueue = new ArrayDeque<Song>();
    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 save");
    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(),
                    mSongQueue.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 artist = promptArtist();
          Song artistSong = promptSongForArtist(artist);
          mSongQueue.add(artistSong);
          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("Unkown choice:  '%s'. Try again. %n%n%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 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++;
    }
    String optionAsString = mReader.readLine();
    int choice = Integer.parseInt(optionAsString .trim());
    System.out.println("Your choice:  ");
    return choice - 1;
  }

  public void playNext() {
   Song song = mSongQueue.poll();
    if (song == null) {
     System.out.println("Sorry there are no songs in the queue. Use choose from the menu to add some"); 
    } else {
     System.out.printf("%n%n%n Open %s to hear %s by %s %n%n%n", 
                       Song.getVideoUrl(), 
                       Song.getTitle(), 
                       Song.getArtist()); 
    }
  }
}```

Thanks in advance.