fetchContact function Dart Flutterflow

Question

Im using FlutterFlow and im implementing a function where it should fetch on the user's device and save all his contacts to show them on a list view.

Dependencies

Issues

The code Im using is this one

// Automatic FlutterFlow imports
import '/backend/backend.dart';
import '/flutter_flow/flutter_flow_theme.dart';
import '/flutter_flow/flutter_flow_util.dart';
import '/custom_code/actions/index.dart'; // Imports other custom actions
import '/flutter_flow/custom_functions.dart'; // Imports custom functions
import 'package:flutter/material.dart';
// Begin custom action code
// DO NOT REMOVE OR MODIFY THE CODE ABOVE!

import 'package:contacts_service/contacts_service.dart';

Future buscarContactos(String? userId) async {
  // Add your function code here!

  List<Contact> contacts = await ContactsService.getContacts();

  final instance = FirebaseFireStore.instance;

  CollectionReference collection =
      instance.collection('users').doc(userId).collection('contacts');

  late Map<String, dynamic> data;
  if (contacts != null)
    data = {
      'contacts': contacts
          .map((k) => {
                if (k.displayName != null) 'name': k.displayName,
                if (k.emails!.isNotEmpty && k.emails != null)
                  'email': k.emails?.first.value,
                if (k.phones!.isNotEmpty && k.phones != null)
                  'phone': k.phones?.first.value
                      .toString()
                      .replaceAll(new RegExp(r"\s\b|\b\s"), "")
                      .replaceAll(new RegExp(r'[^\w\s]+'), '')
                      .replaceAll(new RegExp(r'/^(?!\s*$).+/'), "")
              })
          .toList(),
    };

  collection
      .doc(userId)
      .set(data)
      .then((value) => print("Contacts Updated"))
      .catchError((error) => print("Failed to update Contacts: $error"));
  return userId;
}

I ask the user about the necessary permissions,importing the necessary packages on the code above and implementing neccesary dependencies.