C# WPF System.NullReferenceException. Object reference not set to an instance of an object

Мне необходимо при изменении значения элемента Slider выводить новое значение в Label, но я столкнулся с ошибкой:

Exception thrown: 'System.NullReferenceException' in URCPS.dll
Object reference not set to an instance of an object.

Будто я не инициализировал текстовую метку Label прежде чем использовать её. Вот код:

MainWindow.xaml:

<Window x:Class="URCPS.MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  xmlns:local="clr-namespace:URCPS"
  mc:Ignorable="d"
  Title="MainWindow" Height="475" Width="500">
  <Grid x:Name="grid" HorizontalAlignment="Center" Width="550" Height="434" VerticalAlignment="Bottom">
    <GridSplitter Height="5" HorizontalAlignment="Stretch" VerticalAlignment="Bottom" Margin="0, 0, 0, 60"/>
    <Button x:Name="clickBtn" HorizontalAlignment="Center" VerticalAlignment="Center" Height="340" Width="400" Content="Start" Margin="0, 0, 0, 60" FontSize="35" FontFamily="Arial"/>
    <Slider x:Name="timeSlider" Value="5" Minimum="1" Maximum="60" VerticalAlignment="Bottom" Margin="50, 0, 50, 35" TickPlacement="BottomRight" ValueChanged="SetValue" TickFrequency="2" IsSnapToTickEnabled="True"/>
      <Label x:Name="sliderValueLbl" Content="5" HorizontalAlignment="Center" VerticalAlignment="Bottom" Margin="8" FontSize="15"/>
    </Grid>
</Window>

MainWindow.xaml.cs:

using System;
using System.Windows;

namespace URCPS
{
  public partial class MainWindow : Window
  {

    public MainWindow()
    {
      InitializeComponent();
    }

    private void SetValue(object sender, RoutedPropertyChangedEventArgs<double> e)
    {
      sliderValueLbl.Content = e.NewValue;//здесь вылазит ошибка
    }
  }
}