fix the addTags methods

package com.example.model;

import java.util.List;
import java.util.HashSet;
import java.util.Set;

public class Course {
  private String mTitle;
  private Set<String> mTags;

  public Course(String title) {
    mTitle = title;
    mTags = new HashSet();
    // TODO: initialize the set mTags
  }

  public void addTag(String tag) {
    mTags.put("add", "Add tags");
    // TODO: add the tag
  }

  public void addTags(List<String> tags) {
    mTags.put("add", "add all the tags in the list");
    // TODO: add all the tags passed in
  }

  public boolean hasTag(String tag) {
    // TODO: Return whether or not the tag has been added
    return false;
  }

  public String getTitle() {
    return mTitle;
  }

}