I am trying to implement MVVM into my xamarin app, but it crashes saying 'indexer did not contain closing bracket'

Question

This is part of my xaml code, where the binding happens:

      <ListView  
              ItemsSource="{Binding PenStocks}"
              HasUnevenRows="True"
              ItemSelected="Event_ItemSelected"
              SeparatorVisibility="None"
              Margin="5,5,5,0">
    <ListView.ItemTemplate>

This is the code behind of it:

     public partial class MainPage : ContentPage
    {
    public MainPage()
    {
        InitializeComponent();

        BindingContext = new PenStockListViewModel(new PageService());
    }
    private async void Event_ItemSelected(object sender, SelectedItemChangedEventArgs e)
    {
        await (BindingContext as PenStockListViewModel).PenStockSelected(e.SelectedItem as PenStockViewModel);
    }
    }

This is the viewmodel class of the list, which is the source of the objects that are bound to the listView. (Note: the FillPenstockData and SetRotationData methods are not given to keep it short here)

      class PenStockListViewModel:PenStockBaseViewModel
{
    public ObservableCollection<PenStockViewModel> PenStocks { get; set; } = new ObservableCollection<PenStockViewModel>();

    private PenStockViewModel _selectedPenStock;
    public PenStockViewModel SelectedPenStock
    {
        get
        { return _selectedPenStock; }

        set
        {
            if (_selectedPenStock == value)
                return;

            _selectedPenStock = value;
            OnPropertyChanged();
        }
    }
    private readonly IPageService _ipageService;

    public PenStockListViewModel(IPageService pageService)
    {
        _ipageService = pageService;
        FillPenStockData();
        SetRotationData();
    }

This is the viewmodel class of a single object of PenStock:

       public class PenStockViewModel: PenStockBaseViewModel
{
    public string Name { get; set; }
    public ObservableCollection<Graph> Data { get; set; }

    private double rotations;
    public string Unit { get; set; }
    public double Rotations
    {
        get { return rotations; }

        set
        {
            rotations = value;
        }
    }
}

This is BaseViewModel of Penstock class:

        public class PenStockBaseViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

This is my IPageService interface:

      interface IPageService
{
    Task PushAsync(Page page);
}

This is my PageService class:

     class PageService : IPageService
{
    public async Task PushAsync(Page page)
    {
        await Application.Current.MainPage.Navigation.PushAsync(page);
    }
}

The app works when loaded and the list is loaded perfectly onto the mainpage, but when I select an item, it crashes and enters debugging mode saying 'indexer did not contain closing bracket'. I want it move to the next detail page of the selected item, but doesn't happen. THis is my first app I am using MVVM and I have not fully implemented it yet as I still have remove the event handlers and use ICommand interface. Please help to figure out this error.