Null check operator used on a null value - flutter

Question

body: StreamBuilder(
stream: db.collection('products').where('category', isEqualTo: 'category').snapshots(),
builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
if(snapshot.hasError){
Fluttertoast.showToast(msg: 'Something error');
}
if(snapshot.connectionState == ConnectionState.waiting) {
CircularProgressIndicator();
}
final values = snapshot.data!.docs;
return ListView.builder(
itemCount: values!.length,
itemBuilder: (BuildContext context, int index) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: Container(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text(values![index]['name']),
),
),
);
}
);
},
),
The following _CastError was thrown building StreamBuilder<QuerySnapshot<Map<String, dynamic>>>(dirty, state: _StreamBuilderBaseState<QuerySnapshot<Map<String, dynamic>>, AsyncSnapshot<QuerySnapshot<Map<String, dynamic>>>>#c87c1):

Answer 1

you missed return in your if blocks, so those widgets are not being returned, this redirect to the snapshot.data!.docs widget which is null initially, change it to this:
body: StreamBuilder(
stream: db.collection('products').where('category', isEqualTo: 'category').snapshots(),
builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
if(snapshot.hasError){
Fluttertoast.showToast(msg: 'Something error');
return Text("error"); // add this to showcase the error
}
if(snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator(); // add this to show loading when data is fetching
}
final values = snapshot.data!.docs;
return ListView.builder(
itemCount: values!.length,
itemBuilder: (BuildContext context, int index) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: Container(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text(values![index]['name']),
),
),
);
}
);
},
),