ListView / ImageCell separator

We're trying to add a separator between items in a ListView. Our items are ImageCell objects.

Here is the XAML code I try to use to add a border in the template:

<ListView x:Name="MenuListView"
                  VerticalOptions="FillAndExpand"
                  BackgroundColor="Transparent"
                  ItemTapped="MenuTapped">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <ImageCell Text="{Binding Text}"
                               ImageSource="{Binding ImageSource}"
                               TextColor="#006cb7" />
                    <BoxView WidthRequest="100"
                         HeightRequest="2"
                         Color="#aaaaaa"
                         Scale="100" />
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>

This generates an exception System.ArgumentException: An element with the same key already exists in the dictionary.

Is it something that I am missing?
Also, is there a simpler way to add those separators? I was told they are native, but I don't see them.

See attached files.

We use Xamarin.Forms 1.3 pre-3