Java で Null オブジェクト参照エラーに対して仮想メソッドを呼び出そうとする

package delftstack;

import javax.naming.Context;

public class Main_Player {
  private Context AppContext;
  private SharedPreferences SharedPreferencesSettingsU;
  private SharedPreferences.Editor PreferencesEditorU;
  private static final int PREFERENCE_MODE = 0;
  private static final String UNIQUE_PREFERENCES_FILE = "DemoApp";

  public Player(Context AppContext, String Player_Name) {
    this.AppContext = AppContext;
    Save_Name(Player_Name);
  }

  public void Save_Name(String nValue) {
    SharedPreferencesSettingsU =
        AppContext.getSharedPreferences(UNIQUE_PREFERENCES_FILE, PREFERENCE_MODE);
    PreferencesEditorU = SharedPreferencesSettingsU.edit();
    PreferencesEditorU.putString("keyName", nValue);
    PreferencesEditorU.commit();
  }

  public String Get_Name(Context DemoContext) {
    SharedPreferencesSettingsU =
        DemoContext.getSharedPreferences(UNIQUE_PREFERENCES_FILE, PREFERENCE_MODE);
    String PlayerName = SharedPreferencesSettingsU.getString("keyName", "ANONYMOUS");
    return PlayerName;
  }
}

package delftstack;

import javax.naming.Context;

public class Player_Name extends Activity {
  private EditText Player_Name;
  private Player M_Player;
  public static Context AppContext;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.player_name);
    AppContext = this;
    Player_Name = (EditText) findViewById(R.id.etName);
  }

  public void onC_Confirm(View btnclick) {
    M_Player = new Player(AppContext, String.valueOf(Player_Name.getText()));
    // M_Player.saveName();
    Intent intent = new Intent(Player_Name.this, Game_Play.class);
    startActivity(intent);
  }

  public void onC_testShPref(View btnclick) {
    Intent intent = new Intent(Player_Name.this, Game_Play.class);
    startActivity(intent);
  }

public class Game_Play extends Activity {
  private TextView Welcome_Player;
  private ListView Games_Created;
  private Player M_Player;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.play_game);

    Welcome_Player = (TextView) findViewById(R.id.tvPlayer_Name);
    Welcome_Player.setText("Welcome Back Player, " + String.valueOf(M_Player.getName(this)) + " !");

    Games_Created = (ListView) findViewById(R.id.listCreatedGames);
    Games_Created.setEmptyView(findViewById(R.id.tvNoGames));
  }
}

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String plp.cs4b.thesis.drawitapp.Main_Player.getName()' on a null object reference
    at plp.cs4b.thesis.drawitapp.Game_Play.onCreate(Game_Play.java:20)
    at android.app.Activity.performCreate(Activity.java:5933)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
    ... 10 more

Welcome_Player.setText("Welcome Back Player, " + String.valueOf(M_Player.getName(this)) + " !");

package delftstack;

public class Game_Play extends Activity {
  private TextView Welcome_Player;
  private ListView Games_Created;
  // initialize the M_Player
  private Player M_Player = new Main_Player(AppContext, "");

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.play_game);

    Welcome_Player = (TextView) findViewById(R.id.tvPlayer_Name);
    Welcome_Player.setText("Welcome Back Player, " + String.valueOf(M_Player.getName(this)) + " !");

    Games_Created = (ListView) findViewById(R.id.listCreatedGames);
    Games_Created.setEmptyView(findViewById(R.id.tvNoGames));
  }
}