dialog call fragment android studio

Good night, I'm having problems in calling a dialog fragment in android, with an activity that is encoded in Kotlin, calling a Java-encoded fragment dialog, the NPE error is happening in the line "datePicker = getActivity (). getLayoutInflater (). Could you help me organize this code so I can launch the dialog with a date picker please? CadastroActivity

class CadastroActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_cadastro)

    button_nascimento.setOnClickListener {
        var dataDialog : FragmentDialogDataPicker = FragmentDialogDataPicker()
        dataDialog.show(supportFragmentManager, "Data Fragment")
    }
}
}

Dialog

public class FragmentDialogDataPicker extends DialogFragment {

private DatePicker datePicker;

@NonNull
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {

    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

    //Selecionando o xml de layout
    LayoutInflater inflater = getActivity().getLayoutInflater();

    //Iniciando o datePicker
    datePicker =  getActivity().findViewById(R.id.datepicker_nacimento);
    Calendar calendar = Calendar.getInstance();
    datePicker.init(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH),
            new DatePicker.OnDateChangedListener() {
                @Override
                public void onDateChanged(DatePicker datePicker, int i, int i1, int i2) {
                    //IMPLEMENTANDO A AÇÃO AO SELECIONAR A DATA NO CALENDÁRIO VIEW
                    Toast.makeText(getContext(), datePicker.getDayOfMonth() + " - " +
                            datePicker.getMonth() + " - " + datePicker.getYear(), Toast.LENGTH_SHORT).show();
                }
            });

    //Setando as configurações do dialog
    builder.setView(inflater.inflate(R.layout.fragment_dialog_data_picker, null))
            .setPositiveButton(getString(R.string.selecionar), new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    //Ação ao selecionar a data de nascimento

                }
            });

    return builder.create();
}
}

xml activity

<?xml version="1.0" encoding="utf-8"?>

<EditText
    android:id="@+id/edit_name"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="@string/nome_completo"
    android:inputType="text" />

<EditText
    android:id="@+id/edit_email"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="@string/email"
    android:inputType="textEmailAddress"
    android:layout_marginTop="@dimen/margim_top_edits" />

<Button
    android:id="@+id/button_nascimento"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/data_de_nascimento"
    android:layout_marginTop="@dimen/margim_top_edits"
    android:layout_gravity="center"/>

<Button
    android:id="@+id/button_localizacao"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Habilitar Localização"
    android:layout_gravity="center"
    android:layout_marginTop="@dimen/margim_top_edits"/>

<Button
    android:id="@+id/button_cadastrar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/cadastrar"
    android:layout_marginTop="@dimen/margim_top_edits" />
</LinearLayout>

xml dialog

<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
android:layout_height="match_parent">

<DatePicker
    android:id="@+id/datepicker_nacimento"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

</android.support.constraint.ConstraintLayout>