(Универсальное приложение для Windows) System.NullReferenceException: ссылка на объект не указывает на экземпляр объекта

Когда я пытаюсь запустить очень простое универсальное приложение для Windows, появляется исключение выше. Я пытался несколько раз исправить это, но это все еще там. Я действительно новичок в программировании, поэтому я буду очень рад, если кто-то может помочь. Это дизайн моей главной страницы:

<UserControl x:Class = "simpleCalc.MainPage"
xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local = "using:Test_App"
xmlns:d = "http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable = "d"
Background = "{ThemeResource ApplicationPageBackgroundThemeBrush}"
d:DesignHeight = "300" d:DesignWidth = "400">

    <Grid x:Name = "LayoutRoot" Background = "#FFE2D7CC">
    <TextBlock x:Name = "textBlock" HorizontalAlignment = "Left" Margin = "13,50,0,0" Text = "Километри" 
TextWrapping = "Wrap" VerticalAlignment = "Top" Height = "31" Width = "114" FontFamily = "Times New Roman" 
FontSize = "22" FontWeight = "Bold"
FontStyle = "Italic"/>
    <TextBlock x:Name = "textBlock1" HorizontalAlignment = "Left" Margin = "36,103,0,0" Text = "Литри" 
TextWrapping = "Wrap" VerticalAlignment = "Top" Height = "32" Width = "114" FontFamily = "Times New Roman" 
FontSize = "22" FontWeight = "Bold"
FontStyle = "Italic"/>
    <TextBlock x:Name = "textBlock2" HorizontalAlignment = "Left" Margin = "16,147,0,0" Text = "Консумация" 
TextWrapping = "Wrap" VerticalAlignment = "Top" Height = "31" Width = "114" FontFamily = "Times New Roman" 
FontSize = "22" FontWeight = "Bold"
FontStyle = "Italic"/>
    <TextBox x:Name = "mileage" HorizontalAlignment = "Left" Height = "28" Margin = "149,47,0,0" 
TextWrapping = "Wrap" Text = "100" VerticalAlignment = "Top" Width = "120" Background = "#FFD6F6F9"/>
    <TextBox x:Name = "liters" HorizontalAlignment = "Left" Height = "31" Margin = "149,97,0,0" 
TextWrapping = "Wrap" Text = "10" VerticalAlignment = "Top" Width = "120" Background = "#FFD2EFF1"/>
    <TextBox x:Name = "cons" HorizontalAlignment = "Left" Height = "27" Margin = "149,145,0,0" 
TextWrapping = "Wrap" Text = "10" VerticalAlignment = "Top" Width = "120" Background = "#FFC5EAEE"/>
    <TextBlock x:Name = "textBlock3" HorizontalAlignment = "Left"
Margin = "274,147,0,0" TextWrapping = "Wrap" Text = "1/100 km" VerticalAlignment = "Top"/>


    <Button x:Name = "button1" Content = "ИЗЧИСЛИ" HorizontalAlignment = "Left"
Margin = "149,199,0,0" VerticalAlignment = "Top" Width = "120" Click = "Button_Click"
Height = "35" Foreground = "#FF3A2121" Background = "#FFF32424">
        <Button.BorderBrush>
            <LinearGradientBrush EndPoint = "0.5,1" StartPoint = "0.5,0">
                <GradientStop Color = "#FFA3AEB9" Offset = "0"/>
                <GradientStop Color = "#FF8399A9" Offset = "0.375"/>
                <GradientStop Color = "#FF718597" Offset = "0.375"/>
                <GradientStop Color = "#FFEE3760" Offset = "1"/>
            </LinearGradientBrush>
        </Button.BorderBrush>
    </Button>
</Grid>

</UserControl>

А вот функциональный код:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

namespace simpleCalc
{
    public partial class MainPage : UserControl
    {
       public MainPage()
        {
        InitializeComponent();
        }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        double dMileage = Double.Parse(mileage.Text);
        double dLiters = Double.Parse(liters.Text);
        double dRes = 100 * (dLiters/dMileage);
        cons.Text = dRes.ToString("##.##");
    }
}

} Когда я запускаю приложение (в данном случае это простой расчет топлива), оно выдает исключение:

if (e.PrelaunchActivated == false)
        {
            if (rootFrame.Content == null)
            {
                ***rootFrame.Navigate(typeof(MainPage), e.Arguments);***
            }