_CastError (Null check operator used on a null value) because it requires loading

Question

So I am creating an Instagram clone and when I open the feed screen, an error that says '_CastError (Null check operator used on a null value)' pops up. But when I left it for a minute it was replaced by the feed screen normally So it turns out it wants to load, but I am not sure how can I make it do so.

Here is the code(The bolded line is the one that requires time):

`

class PostCard extends StatefulWidget {`
`final snap;`
`const PostCard({Key? key, required this.snap}) : super(key: key);`

`@override`
`State<PostCard> createState() => _PostCardState();`
`}`

`class _PostCardState extends State<PostCard> {`
`bool isLikeAnimating = false;`
`int commentLen = 0;`
`bool isLoading = false;`

`@override`
`Widget build(BuildContext context) {`
`

    ** final UserProvider userProvider = Provider.of<UserProvider>(context);**`


`return isLoading`


`? const Center(`


`child: CircularProgressIndicator(),`


`)`
`: Container(`


`color: Colors.white,`


`padding: EdgeInsets.symmetric(vertical: 10),`


`child: Column(`


`children: [`


`Container( //inside here are the contents of the post`
`);`
`}`
`}`

`Feed Screen:`
`StreamBuilder(`


`stream: stream,`


`builder: (context,`


`AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>> snapshot) {`


`if (snapshot.connectionState == ConnectionState.waiting) {`


`return Center(`


`child: CircularProgressIndicator(),`


`);`


`}`


`return ListView.builder(`


`itemCount: snapshot.data!.docs.length,`


`itemBuilder: (context, index) => PostCard(`


`snap: snapshot.data!.docs[index],`


`),`
`);`
`}));`