calender dialog button onclick: 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Question

I understand this question has been asked many times. but most of them are specific. In my case, tried all the fixes I could. Any help appreciated? p.s. I am a beginner and I have not shown some code from java that I am sure that it doesnt affect the issue here. Also the main function I am aiming to do is, to open a dialog box with a calender to pick a date when user clicks a button (btn_pf_dob), and when user selects it, the chosen date is displayed on the same button.

Error:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.name.appname/com.example.name.appname.ProfileDetailsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Java:

public class ProfileDetailsActivity extends AppCompatActivity {
Button selectpfbirthdate;
    DatePickerDialog datePickerDialog;
    int year;
    int month;
    int dayOfMonth;
    Calendar calendar;

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

selectpfbirthdate = findViewById(R.id.btn_pf_dob);

        selectpfbirthdate.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                calendar = Calendar.getInstance();
                year = calendar.get(Calendar.YEAR);
                month = calendar.get(Calendar.MONTH);
                dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
                datePickerDialog = new DatePickerDialog(ProfileDetailsActivity.this,
                        new DatePickerDialog.OnDateSetListener() {
                            @Override
                            public void onDateSet(DatePicker datePicker, int year, int month, int day) {
                                selectpfbirthdate.setText(day + "/" + (month + 1) + "/" + year);
                            }
                        }, year, month, dayOfMonth);
                //datePickerDialog.getDatePicker().setMinDate(System.currentTimeMillis());
                datePickerDialog.show();
            }
        });


    }

XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:background="@color/colorPrimaryDark"
    style="@style/traNav"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".ProfileDetailsActivity">
<ScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">
<TableLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:stretchColumns="1"
                android:background="@color/colorPrimaryDark">
<TableRow
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_margin="3dp"
                    android:layout_weight="1"
                    android:orientation="vertical">

                    <android.support.v7.widget.AppCompatTextView
                        android:layout_weight="1"
                        android:gravity="start"
                        android:padding="10dip"
                        android:text="@string/date_of_birth"
                        android:textColor="@android:color/background_light"
                        android:textSize="18sp"
                        />

                    <Button
                        style="@style/et_background"
                        android:layout_height="match_parent"
                        android:layout_weight="1"
                        android:textAlignment="center"
                        android:gravity="start"
                        android:padding="10dip"
                        android:textColor="@android:color/background_dark"
                        android:background="#d3d4d5"
                        android:textSize="18sp"
                        android:hint="@string/pick_date"
                        android:textAllCaps="false"
                        android:id="@+id/selectpfbirthdate"/>

                </TableRow>
</TableLayout>
</LinearLayout>
<Scrollview>
</LinearLayout>

EDIT: My bad, I use the wrong ID. Thank you.