ActionBar back button crash my app - android-actionbar

Question

I have problem with my school project when I want to back to my CurentCourseActivity using back button form action bar I have NE
Attempt to invoke virtual method 'java.util.List `com.example.pingu.mylanguages.Language.getList()' on a null object reference at
com.example.pingu.mylanguages.CurentCourseActivity.onCreate(CurentCourseActivity.java:37)`
While I use normal back button problem is not appear.
When we choose Lesson from GridView that makes a new activity. When we choose the back button from ActionBar then I have NE.
CourentCourseActivity:
public class CurentCourseActivity extends AppCompatActivity {
private Language language;
#Override
protected void onCreate(Bundle savedInstanceState) {
Log.d("s","onCreate");
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_curent_course);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
if (savedInstanceState!=null){
language = (Language) savedInstanceState.getSerializable("Lang");
Log.d("xx","Coś ma");
}
if (getIntent().getExtras() != null) {
language = (Language) getIntent().getSerializableExtra("Lang"); //Obtaining data
}
GridView grid = (GridView) findViewById(R.id.grid);
CurrentCourseAdapter adapter = new CurrentCourseAdapter(this, R.layout.grid_item_curent_course, language.getList());
grid.setAdapter(adapter);
grid.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
Intent intent = new Intent(CurentCourseActivity.this,LessonActivity.class);
intent.putExtra("Lesson",(Lesson)language.getList().get(i));
startActivity(intent);
}
});
getSupportActionBar().setTitle(language.getName());
}
}
LessonActivity:
public class LessonActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lesson);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
if(getIntent().getExtras()!=null){
Lesson lesson = (Lesson) getIntent().getSerializableExtra("Lesson");
getSupportActionBar().setTitle(lesson.getNamel());
}
}
}

Answer 1

The answer is simplest then I expect. So I need to overide this button and do it as normal back button because ActrionBar back button destroy parent activity.
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
onBackPressed();
return true;
}
return super.onOptionsItemSelected(item);
}