如何修复片段中来自registerReceiver()的null返回，以及活动中正在运行的相同代码

public class MyActivity extends AppCompatActivity {
    private BroadcastReceiver myReceiver;

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

        // 创建广播接收器
        myReceiver = new MyReceiver();

        // 注册广播接收器
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
        registerReceiver(myReceiver, intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        // 注销广播接收器
        unregisterReceiver(myReceiver);
    }

    // 自定义广播接收器
    private class MyReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            // 处理接收到的广播
        }
    }
}