is there a way to help me fix the type null is not a subtype of type Map<string, dynamic>?-CodePudding

I have been working on flutter for few months now, and I got to understand how to fix null safety issues but this one is really complicated for me and i would like to get helped.

Here is my problem:

Whenever I am trying to sign in, I am getting this error: 'Null' type is not a subtype of type Map<string, dynamic> I tried my best to figure out what goes wrong but I am unable, any help will be a life saving...

import 'package:cloud_firestore/cloud_firestore.dart';

class User {
 final String email;
 final String uid;
 final String photoUrl;
 final String username;
 final String bio;
 final List followers;
 final List following;

const User({
  required this.email,
  required this.uid,
  required this.photoUrl,
  required this.username,
  required this.bio,
  required this.followers,
  required this.following,
 });

then i continued here

Map<String, dynamic> toJson() => {
    "username": username,
    "uid": uid,
    "email": email,
    "photoUrl": photoUrl,
    "bio": bio,
    "followers": followers,
    "following": following,
  };

   static User fromSnap(DocumentSnapshot snap) {
   var snapshot = snap.data() as Map<String, dynamic>;

  return User(
     username: snapshot['username'],
     uid: snapshot['uid'],
     email: snapshot['email'],
     photoUrl: snapshot['photoUrl'],
     bio: snapshot['bio'],
     followers: snapshot['followers'],
     following: snapshot['following'],
      );
     }
    }

now I am getting the error on this line: null type is not a subtype of Map<string, dynamic>

var snapshot = snap.data() as Map<String, dynamic>;

this is all my problem, thanks in advance.

CodePudding user response：

Your snapshot value is nullable and you try to cast it to map, instead of this:

var snapshot = snap.data() as Map<String, dynamic>;

try this:

var snapshot = snap.data() != null ? snap.data() as Map<String, dynamic> : {};

Also change your return to this:

return User(
     username: snapshot['username']??””,
     uid: snapshot['uid'] ??””,
     email: snapshot['email'] ??””,
     photoUrl: snapshot['photoUrl'] ??””,
     bio: snapshot['bio'] ??””,
     followers: snapshot['followers'] ??[],
     following: snapshot['following'] ??[],
  );