CommandParameter is null if button activated by InputGesture

<Window x:Class="WpfApplication1.Window2"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window2" Height="600" Width="600" xmlns:apr="clr-namespace:ActiproSoftware.Windows.Controls.Ribbon;assembly=ActiproSoftware.Ribbon.WPF30" xmlns:apc="clr-namespace:ActiproSoftware.Windows.Controls.Ribbon.Controls;assembly=ActiproSoftware.Ribbon.WPF30" xmlns:aps="clr-namespace:ActiproSoftware.Windows.DocumentManagement;assembly=ActiproSoftware.Shared.WPF30">
        
    <StackPanel>
        <apr:Ribbon Name="ribbon" DockPanel.Dock="Top">
            <apr:Ribbon.ApplicationMenu>
                <apc:ApplicationMenu KeyTipAccessText="">
                    <apc:ApplicationMenu.AdditionalContent>
                        <apc:RecentDocumentMenu Label="Recent Projects">
                            <aps:RecentDocumentManager x:Name="recentDocumentManager" />
                        </apc:RecentDocumentMenu>
                    </apc:ApplicationMenu.AdditionalContent>
                </apc:ApplicationMenu>
            </apr:Ribbon.ApplicationMenu>
        </apr:Ribbon>
    </StackPanel>
</Window>

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using ActiproSoftware.Windows.Controls.Ribbon.Controls;
using Button = ActiproSoftware.Windows.Controls.Ribbon.Controls.Button;
using ActiproSoftware.Windows.Controls.Ribbon.Input;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window2.xaml
    /// </summary>
    public partial class Window2 : Window
    {
        public Window2()
        {
            InitializeComponent();
            Loaded += new RoutedEventHandler(Window2_Loaded);
        }

        void Window2_Loaded(object sender, RoutedEventArgs e)
        {
            ribbon.Tabs.Add(new Tab());
            ribbon.Tabs[0].Items.Add(new Group());

    
            RibbonCommand command = new RibbonCommand("button command", GetType());
            command.InputGestures.Add(new KeyGesture(Key.F4, ModifierKeys.None));
            Button button = new Button();
            button.CommandParameter = "param";
            button.Label = "button";
            ribbon.Tabs[0].Items[0].Items.Add(button);

            button.Command = command;

            CommandBinding binding = new CommandBinding(command, Execute);
            CommandBindings.Add(binding);
        }

        void Execute(object sender, ExecutedRoutedEventArgs e)
        {
            string x = (string) e.Parameter; 
        }
    }
}