How can I insert an initial element into Listview.builder

I want to show the defaultUserContainer() in case the stream is empty but also in case it's not, as an initial element of the list. Currently. I can't seem to make either scenarios work. How can I design this better?

Column(
          children: [
            Row(
              children: [
                Padding(
                  padding: const EdgeInsets.only(left: 16.0, top: 8.0),
                  child: Padding(
                    padding: const EdgeInsets.only(bottom: 8.0),
                    child: Align(
                        alignment: Alignment.centerLeft,
                        child: Text(
                          "users",
                          style:
                          TextStyle(fontSize: 20.0, color: Colors.black87),
                        )),
                  ),
                ),
              ],
            ),
            SizedBox(
              height: 120,
              child: FutureBuilder(
                builder: (context, snapshot) {
                  return StreamBuilder(
                    stream: _firestore.collection('ts').where('userid', isEqualTo: widget.user.id).snapshots(),
                      builder: (context, snapshot) {
                        if (!snapshot.hasData) {
                           defaultUserContainer();  //If there's no users. tried returning it, or doing like it is here. never shows
                           return Text("");
                        } else {
                          return ListView.builder(
                            scrollDirection: Axis.horizontal,
                            itemCount: snapshot.data.documents.length,
                            itemBuilder: (BuildContext context, int index) {
                              DocumentSnapshot userDoc = snapshot.data.documents[index];
                              if(index < snapshot.data.documents.length){
                                return Padding(
                                  padding: const EdgeInsets.only(bottom: 8.0, left: 8.0, right: 8.0),
                                  child: GestureDetector(
                                    onTap: () => {},
                                    child: Container(
                                        child: FittedBox(
                                            child: Material(
                                              color: Colors.white,
                                              elevation: 4.0,
                                              borderRadius:
                                              BorderRadius.circular(8.0),
                                              shadowColor: Colors.grey,
                                              child: Row(
                                                children: <Widget>[
                                                  Container(
                                                    child: myDetailsContainer(userDoc),  //This guy works. it's just a more complicated defaultuserContainer()
                                                  ),
                                                ],
                                              ),
                                            )
                                        )
                                    ),
                                  ),
                                );
                              }
                              return ListTile(leading:defaultuserContainer()); //Doesn't show when there's users users (my goal is to always have this as an initial item)
                          });
                         }
                        },
                      );
                     },
                    ),
                  )
                 ]
                );
    
        Widget defaultUserContainer() {
        return ClipRRect(
          borderRadius: BorderRadius.circular(8),
          child: Container(
            height: 120,
            width: 120,
            color: myColors.blue,
            child: Center(child: Icon(Icons.add, size: 65, color: Colors.white,)),
          ),
        );
      }

Read more here: https://stackoverflow.com/questions/66332525/how-can-i-insert-an-initial-element-into-listview-builder