Anyone can find the error?

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity {

  public static final String EXTRA_YEAR = "EXTRA_YEAR";
  public static final String EXTRA_ENERGY = "EXTRA_ENERGY";

  public Button goButton;
  public EditText yearField;

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

    goButton = (Button)findViewById(R.id.goButton);
    yearField = (EditText)findViewById(R.id.yearField);

    final EnergySource source = new EnergySource();

    goButton.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        // Add your code in here!
        Intent intent = new Intent(MainActivity.this, TimeTravelActivity.class);
        intent.putExtra(EXTRA_YEAR, yearField.getText().toString());
        intent.putExtra(EXTRA_ENERGY, source);
        startActivity(intent);
      }
    });
  }
}

import android.os.Bundle;
import android.view.View;

public class TimeTravelActivity extends Activity {

  public String targetYear;
  EnergySource energySource;

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

    Intent intent = getIntent();
    targetYear = intent.getStringExtra(MainActivity.EXTRA_YEAR);
    if(intent.getParcelableExtra(MainActivity.EXTRA_ENERGY) != null){
      energySource = intent.getParcelableExtra(MainActivity.EXTRA_ENERGY);
    }
  }
}