I want to get data from firebase cloud
Data means my chatApp's messages.

[![like this I want to print messages on my screen](https://i.stack.imgur.com/b9Qp2.png)](https://i.stack.imgur.com/b9Qp2.png)

but in my code i got error
[![see this arrow line in both images](https://i.stack.imgur.com/F8PFP.png)](https://i.stack.imgur.com/F8PFP.png)

android studio suggest me to add nullcheck(!) to

final messages = snapshot.data!.documents;

but it not working