Vertical viewport was given unbounded height. flutter

Question

I'm trying to generate a list of ExpansionTiles that has another list of ExpansionTiles as children. The lists are generated by receiving data from the database. The problem is that when I click on an ExpansionTile it gives me this error and it doesn't expand:

The following assertion was thrown during performResize(): Vertical viewport was given unbounded height. Viewports expand in the scrolling direction to fill their container. In this case, a vertical viewport was given an unlimited amount of vertical space in which to expand. This situation typically happens when a scrollable widget is nested inside another scrollable widget.

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Center(child: Text('MAGAZZINO',
            style: TextStyle(fontWeight: FontWeight.bold))),
      ),
      body: _error != ""
          ? Center(child: Text('Error: $_error'),)
          : ListView.builder(
        controller: _scrollController,
        itemCount: _list.length + (_isLoading ? 1 : 0),
        itemBuilder: (BuildContext context, int i) {
          if (i == _list.length) {
            return const Center(child: CircularProgressIndicator());
          } else {
            return Container(
              child: ExpansionTile(
                leading: CircleAvatar(child: Text("${_list[i].sommaCodici()}")),
                title: Text("BANCALE: ${_list[i].getBancale()}"),
                subtitle: Text("data creazione: ${_list[i].getData()}"),
                children: <Widget>[
                    ListView.builder(
                        itemCount: _list[i].sommaCodici(),
                        scrollDirection: Axis.vertical,
                        itemBuilder: (BuildContext context, int j){
                            child: Card(
                                  child: ExpansionTile(
                                    onExpansionChanged: (bool change) {
                                    },
                                    leading: CircleAvatar(child: Text("${_list[i].getnPezziC()[j]}")),
                                    title: Text("codice: ${_list[i].getCodiciC()[j]}"),
                                    subtitle: Text("data: ${_list[i].getDateC()[j]}"),
                                    children: <Widget>[
                                      Expanded(
                                        child: ButtonBar(
                                          alignment: MainAxisAlignment.spaceAround,
                                          buttonHeight: 52.0,
                                          buttonMinWidth: 90.0,
                                          children: <Widget>[
                                            Expanded(
                                              child: TextButton(
                                                style: flatButtonStyle,
                                                onPressed: () {
                                                  VaiImpegna(DMag(_list[i].getCodiciC()[j], _list[i].getBancale(),
                                                      _list[i].getnPezziC()[j], _list[i].getDateC()[j]));
                                                },
                                                child: const Column(
                                                  children: <Widget>[
                                                    Icon(Icons.arrow_downward),
                                                    Padding(
                                                      padding: EdgeInsets.symmetric(vertical: 2.0),
                                                    ),
                                                    Text('Impegna'),
                                                  ],
                                                ),
                                              ),
                                            ),
                                            Expanded(
                                              child: TextButton(
                                                style: flatButtonStyle,
                                                onPressed: () {
                                                  VaiResi(DMag(_list[i].getCodiciC()[j], _list[i].getBancale(),
                                                      _list[i].getnPezziC()[j], _list[i].getDateC()[j]));
                                                },
                                                child: const Column(
                                                  children: <Widget>[
                                                    Icon(Icons.arrow_upward),
                                                    Padding(
                                                      padding: EdgeInsets.symmetric(vertical: 2.0),
                                                    ),
                                                    Text('Reso'),
                                                  ],
                                                ),
                                              ),
                                            ),
                                            Expanded(
                                              child: TextButton(
                                                style: flatButtonStyle,
                                                onPressed: () {
                                                },
                                                child: const Column(
                                                  children: <Widget>[
                                                    Icon(Icons.swap_vert),
                                                    Padding(
                                                      padding: EdgeInsets.symmetric(vertical: 2.0),
                                                    ),
                                                    Text('Elimina'),
                                                  ],
                                                ),
                                              ),
                                            ),
                                          ],
                                        ),
                                      ),
                                    ],
                                  ),
                            );
                        }
                    ),
                ],
              ),
            );
          }
        },
      ),
    );
  }

I try to add expanded widgets but didn't worked. the only thing that worked was using a Container and giving it an accurate height. But it can't be a valid solution since I can't know how long the list could be.