Handle null value in Dart / Flutter

Question

I have this User class and then a Firestore Document, that may or may not contain a photoURL or some other values. The problem is, that when I try to create an user I get this exception because some of the values are Null.

I've tried to handle it like this:

var photoURL = snapshot.data['photoURL']  ??= '';

but it seems it doesn't work.

Can anyone explain best practices handling Null values in Dart/Flutter respectively?

EDIT: I'm checking if snapshot.exists before and if I create the user omitting the values I know are Null, it creates it properly.

EDIT 2: I've found the problem appears when I try to handle empty List like this:

var favorites =  snapshot.data['favorites'] ?? [''];

are you doing snapshot.hasData check before looking for 'photoURL' ? — Harsh Bhikadia
– Harsh Bhikadia, Commented Sep 13, 2019 at 15:06
i've tried this before and it doesn't work, then I've read this article medium.com/@thinkdigitalsoftware/… and I've changed it to ??= — i6x86
– i6x86, Commented Sep 13, 2019 at 15:25

i6x86 · Accepted Answer · 2019-09-13 15:59:25Z

3

It seems I was initialized the value the wrong way when I converted it to Json.

I handle the empty Array like this

Map<String, dynamic> toJson() => {
   'favorites' : favorites ?? '',
}

when it should be:

Map<String, dynamic> toJson() => {
   'favorites' : favorites ?? [''],
}

So it was throwing when I tried to assign an empty Array to String.

answered Sep 13, 2019 at 15:59

i6x86

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1 Comment

Ivo Over a year ago

just so you know [''] is not an empty array. It's an array containing 1 element, an empty string. An empty array would be []

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