ERROR

package com.example.model;

import java.util.List;

public class Course {
  private String mName;
  private List<Video> mVideos; 

  public Course(String name, List<Video> videos) {
    mName = name;
    mVideos = videos;
  }

  public String getName() {
    return mName;
  }

  public List<Video> getVideos() {
    return mVideos;
  }

}

package com.example.model;

public class Video {
  private String mTitle;

  public Video(String title) {
    mTitle = title;
  }

  public String getTitle() {
    return mTitle;
  }

  public void setTitle(String title) {
    mTitle = title;
  }

}

import com.example.model.Course;
import com.example.model.Video;
import java.util.List;
import java.util.TreeMap;
import java.util.Map;

public class QuickFix {

  public void addForgottenVideo(Course course) {
    List<Video> videoList = course.getVideos();
    Video video = new Video("The Beginning Bits");

    videoList.add(1, video);

  }

  public void fixVideoTitle(Course course, String oldTitle, String newTitle) {
      if (videoTitleMap.containsKey(oldTitle)) {
          Video video = videoTitleMap.get(oldTitle);
            video.setTitle(newTitle);
        videoTitleMap.remove(oldTitle);
    }
  }

  public Map<String, Video> videosByTitle(Course course) {
    //Map<String, Video> videoTitleMap = new TreeMap<String, Video>();
    List<Video> videoList = course.getVideos();
    for (Video video : videoList) {
     videoTitleMap.put(video.getTitle(), video);
       } 
return videoTitleMap;
  }
}