Widget _buildMenuItem(BuildContext context, MenuItem item) {
    return ExpansionTile(
      title: Text(item.title),
      children: _buildSubMenu(context, item.children),
    );
  }

List<Widget>? _buildSubMenu(BuildContext context, List<MenuItem>? children) {
    if (children == null) {
      return null;
    }

    return children.map((child) {
      if (child.children != null) {
        return _buildMenuItem(context, child);
      } else {
        return ListTile(
          title: Text(child.title),
          onTap: () {
            Navigator.of(context).pop(); // Close the drawer
            if (child.routeName != null) {
              Navigator.pushNamed(context, child.routeName!);
            }
          },
        );
      }
    }).toList();
  }

This is the one page code of nested side menu in flutter every thing is working fine but I’m getting error here

The argument type 'List<Widget>?' can't be assigned to the parameter type 'List<Widget>'.
I’m new bee in flutter please help if possible
Thank you…!