GetSerializableExtra returning null

I need a little help to solve the following question.

I have two activities, A and B. The activity A start B for result, and B sends back to A a serializable object.

Activity a starting activity B:

    ...
    Intent intent = new Intent(MainActivity.this, ExpenseActivity.class);       
    startActivityForResult(intent, EXPENSE_RESULT);  
    ...

Activity B sending data to A:

    ...
    ExpensePacket packet = new ExpensePacket();
    ...
    Intent returnIntent = new Intent();
    returnIntent.putExtra(MainActivity.PACKET_INTENT,packet);
    setResult(RESULT_OK,returnIntent);     
    finish();

Point where the activity A gets the data sent from B:

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == EXPENSE_RESULT) {
        if(resultCode == RESULT_OK){                
            ExpensePacket result = (ExpensePacket)getIntent().getSerializableExtra(PACKET_INTENT);

            wallet.Add(result);
            PopulateList();
        }
        else{
             //Write your code otherwise
        }
    }
}    

My Serializable object, the one who is sent from B to A:

class ExpensePacket implements Serializable {

    private static final long serialVersionUID = 1L;    
    private Calendar calendar;  

    public void SetCalendar(Calendar aCalendar){
        calendar = aCalendar;
    }

    public Calendar GetCalendar(){
        return calendar;
    }

    public String GetMonthYear() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy");
        sdf.format(calendar.getTime());                 

        String returnString = "";
        returnString += sdf.toString();
        returnString += "/";
        returnString += Functions.GetMonthName(calendar);

        return sdf.toString();
    }   
}

Somebody can help me to figure out why the data sent from B t