DatePickerDialog and LocalDate.parse crashes app in Android Studio

I'm working on a project where I want to make an app which has some kind of calendar.

Because I think a datepicker is a handy tool, I want to uses this. When the date is picked, the CalendarUtils.selectedDate has to change to in order to change the week view. To let this work, I have to make a LocalDate from a string (output datepicker).

Unfortunately my app only makes it 50% of the times when the datepicker is used. Sometimes it works, sometimes it doesn't. I'm fairy certain it has something to do with this line

LocalDate localDate = LocalDate.parse(date_string, formatter);

because when I just use a string to display the date (and skip the updating weekview) it works all the time.

Someone who can help me or know a way to bypass this problem?

My code:

package codewithcal.au.calendarappexample;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ListView;
import android.widget.TextView;
import android.app.DatePickerDialog;

import java.time.LocalDate;
import java.util.ArrayList;

import static codewithcal.au.calendarappexample.CalendarUtils.daysInWeekArray;
import java.time.format.DateTimeFormatter;
import java.time.LocalDateTime;


public class WeekViewActivity extends AppCompatActivity implements CalendarAdapter.OnItemListener
{
    private TextView monthYearText;
    private RecyclerView calendarRecyclerView;
    private ListView eventListView;
    TextView dateView;
    DatePickerDialog picker;


    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_week_view);
        initWidgets();
        CalendarUtils.selectedDate = LocalDate.now();
        setWeekView();

        // datepicker

        dateView = findViewById(R.id.monthYearTV);
        dateView.setOnClickListener(v -> {
            picker = new DatePickerDialog(WeekViewActivity.this,
                    (view, year, monthOfYear, dayOfMonth) -> {
                        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
                        String date_string = dayOfMonth + "/" + (monthOfYear + 1) + "/" + year;
                        LocalDate localDate = LocalDate.parse(date_string, formatter);
                        CalendarUtils.selectedDate = localDate;
                        setWeekView();
                        dateView.setText(localDate.format(formatter));
                    }, CalendarUtils.selectedDate.getYear(), CalendarUtils.selectedDate.getMonthValue()-1, CalendarUtils.selectedDate.getDayOfMonth());
            picker.show();
        });
    }

    private void initWidgets()
    {
        calendarRecyclerView = findViewById(R.id.calendarRecyclerView);
        monthYearText = findViewById(R.id.monthYearTV);
        eventListView = findViewById(R.id.eventListView);
    }

    private void setWeekView()
    {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        LocalDateTime now = LocalDateTime.now();
        monthYearText.setText(dtf.format(now));
        ArrayList<LocalDate> days = daysInWeekArray(CalendarUtils.selectedDate);

        CalendarAdapter calendarAdapter = new CalendarAdapter(days, this);
        RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getApplicationContext(), 7);
        calendarRecyclerView.setLayoutManager(layoutManager);
        calendarRecyclerView.setAdapter(calendarAdapter);
        setEventAdpater();
    }


    public void previousWeekAction(View view)
    {
        CalendarUtils.selectedDate = CalendarUtils.selectedDate.minusWeeks(1);
        setWeekView();
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        monthYearText.setText(dtf.format(CalendarUtils.selectedDate));
    }

    public void nextWeekAction(View view)
    {
        CalendarUtils.selectedDate = CalendarUtils.selectedDate.plusWeeks(1);
        setWeekView();
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        monthYearText.setText(dtf.format(CalendarUtils.selectedDate));
    }

    @Override
    public void onItemClick(int position, LocalDate date)
    {
        CalendarUtils.selectedDate = date;
        setWeekView();
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/yyyy");
        monthYearText.setText(dtf.format(date));
    }

    @Override
    protected void onResume()
    {
        super.onResume();
        setEventAdpater();
    }

    private void setEventAdpater()
    {
        ArrayList<Event> dailyEvents = Event.eventsForDate(CalendarUtils.selectedDate);
        EventAdapter eventAdapter = new EventAdapter(getApplicationContext(), dailyEvents);
        eventListView.setAdapter(eventAdapter);
    }

    public void newEventAction(View view)
    {
        startActivity(new Intent(this, EventEditActivity.class));
    }
}

package codewithcal.au.calendarappexample;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.util.List;

public class EventAdapter extends ArrayAdapter<Event>
{
    public EventAdapter(@NonNull Context context, List<Event> events)
    {
        super(context, 0, events);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent)
    {
        Event event = getItem(position);

        if (convertView == null)
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.event_cell, parent, false);

        TextView eventCellTV = convertView.findViewById(R.id.eventCellTV);

        String eventTitle = event.getName() +" "+ CalendarUtils.formattedTime(event.getTime());
        eventCellTV.setText(eventTitle);
        return convertView;
    }
}

A screen from how the interface looks: