Binding in code

Hi, in this documentation https://documentation.devexpress.com/#Xamarin/clsDevExpressMobileDataGridTemplateColumntopic there are example code for binding using devexpress gridcontrol. In the Xaml:MainPage.xaml tab could someone explain this binding:

 <Grid BindingContext="{Binding Source}" Padding="0,15,0,15">

and how to do this in code?
I have tried the following:

templateColumn.DisplayTemplate = new DataTemplate (() => {

    Label firstNameLabel = new Label();
    firstNameLabel.FontAttributes = FontAttributes.Bold;
    firstNameLabel.FontSize = 20;
    firstNameLabel.SetBinding(Label.TextProperty, new Binding("FirstName"));

    Label emailLabel = new Label();
    emailLabel.SetBinding(Label.TextProperty, new Binding("Email"));

    Grid grid = new Grid {

        RowDefinitions = {
            new RowDefinition() { Height = GridLength.Auto },
            new RowDefinition() { Height = GridLength.Auto }
        },
        Children = {
            firstNameLabel,
            emailLabel
        }
    };

    grid.SetBinding(Grid.BindingContextProperty, new Binding("Source"));

    return grid;
});

but I keep getting this error:

System.NullReferenceException: Object reference not set to an instance of an object
  at at DevExpress.Mobile.DataGrid.Internal.ObjectRowData