Problem with data.data code for information retrieval in firebase

good evening sir, ladies, I have an error that I can't resolve despite the tips I got on the net. please guide me.
I am told this: The method 'data' can't be unconditionally invoked because the receiver can be 'null'.
Try making the call conditional (using '?.') or adding a null check to the target ('!').
the error is in Map _productMap = productSnap.data.data();
    if (productSnap.connectionState ==
                            ConnectionState.done) {
                          Map _productMap = productSnap.data.data();

                          return Container(
                            decoration: BoxDecoration(
                              borderRadius: BorderRadius.circular(12.0),
                            ),
                            // height: 350.0,
                            margin: EdgeInsets.symmetric(
                              upright: 12.0,
                              horizontal: 24.0,
                            ),
                            /*child: Text("Name: ${document['name']}"),*/
                            child:Container(
                              child: Text("${_productMap['name']}"),
                            ),
                          );
                        }

Here is the full code:
//import 'dart:html';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:djasse_application/ecran/product_page.dart';
import 'package:djasse_application/services/firbase_services.dart';
import 'package:djasse_application/widget/custon_action_bar.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/src/foundation/key.dart';
import 'package:flutter/src/widgets/framework.dart';

import '../constant.dart';

class cartpage extends StatefulWidget {
  const cartPage({Key? key}): super(key: key);

  @override
  State<pagePanier> createState() => _pagePanierState();
}

class _pageCartState extends State<pageCart> {
  /*final CollectionReference _productRef =
      FirebaseFirestore.instance.collection("Users");*/

  FirebaseServices _firebaseServices = FirebaseServices();

  @override
  widget build(BuildContext context) {
    return Scaffold(
        body: Stack(
      children: [
        FutureBuilder<QuerySnapshot>(
          future: _firebaseServices.userRef
              .doc(_firebaseServices.getUserId())
              .collection("Basket")
              .get(),
          builder: (context, snapshot) {
            if (snapshot. hasError) {
              return Scaffold(
                body: Center(
                  child: Text("Error: ${snapshot.error}"),
                ),
              );
            }
            //collection Data ready to be displayed
            if (snapshot. connectionState == ConnectionState. done) {
              //Display data in a list view
              return ListView(
                padding: EdgeInsets.only(
                  high: 108.0,
                  bottom: 12.0,
                ),
                children: snapshot.data!.docs.map((document) {
                  return GestureDetector(
                    /*Click to display image or image info in another page */
                    onTap: () {
                      Navigator.push(
                        background,
                        MaterialPageRoute(
                          builder: (context) => ProductPage(
                            productId: document.id,
                          ),
                        ),
                      );
                    },
                    child: FutureBuilder(
                      future:
                          _firebaseServices.productRef.doc(document.id).get(),
                      builder: (context, productSnap) {
                        /*Map _productMap = productSnap.data.data();*/
                        if (productSnap. hasError) {
                          return Container(
                            child: Center(
                              child: Text("${productSnap.error}"),
                            ),
                          );
                        }
                        if (productSnap.connectionState ==
                            ConnectionState.done) {
                          final _productMap = productSnap.data.data();

                          return Container(
                            decoration: BoxDecoration(
                              borderRadius: BorderRadius.circular(12.0),
                            ),
                            // height: 350.0,
                            margin: EdgeInsets.symmetric(
                              upright: 12.0,
                              horizontal: 24.0,
                            ),
                            /*child: Text("Name: ${document['name']}"),*/
                            child:Container(
                              child: Text("${_productMap['name']}"),
                            ),
                          );
                        }
                      },
                    ),
                  );
                }).toList(),
              );
            }

            //Loading state
            return const Scaffold(
              body: Center(
                child: CircularProgressIndicator(
                  valueColor: AlwaysStoppedAnimation<Color>(
                      Color.fromARGB(255, 243, 159, 80)),
                ),
              ),
            );
          },
        ),
        CustomActionBar(
            title: "Basket",
            hasBackArrow: true,
            hasTitle: true,
            hasBackground: false)
      ],
    ));
  }
}