Проблема с NullReferenceException, C#, WPF

Есть вот такой участок кода XAML:

<TextBox Name="CustomIdeologyNameTextBox1" HorizontalAlignment="Left" Height="32" Margin="480,271,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="125" FontSize="15" Text="Своя идеология1" TextChanged="CustomIdeologyNameTextBox1_TextChanged"/>
<TextBox Name="CustomIdeologyNameTextBox2" HorizontalAlignment="Left" Height="32" Margin="480,310,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="125" FontSize="15" Text="Своя идеология2" TextChanged="CustomIdeologyNameTextBox2_TextChanged"/>
<TextBox Name="CustomIdeologyNameTextBox3" HorizontalAlignment="Left" Height="32" Margin="480,349,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="125" FontSize="15" Text="Своя идеология3" TextChanged="CustomIdeologyNameTextBox3_TextChanged"/>
<TextBox Name="CustomIdeologyNameTextBox4" HorizontalAlignment="Left" Height="32" Margin="480,387,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="125" FontSize="15" Text="Своя идеология4" TextChanged="CustomIdeologyNameTextBox4_TextChanged"/>
<ComboBox HorizontalAlignment="Left" Height="28" Margin="480,432,0,0" VerticalAlignment="Top" Width="120">
            <TextBlock>Демократия</TextBlock>
            <TextBlock>Коммунизм</TextBlock>
            <TextBlock>Фашизм</TextBlock>
            <TextBlock>Нейтралитет</TextBlock>
            <TextBlock Name="ComboBoxCustomIdeology1" Text="Своя идеология 1"></TextBlock>
            <TextBlock Name="ComboBoxCustomIdeology2" Text="Своя идеология 2"></TextBlock>
            <TextBlock Name="ComboBoxCustomIdeology3" Text="Своя идеология 3"></TextBlock>
            <TextBlock Name="ComboBoxCustomIdeology4" Text="Своя идеология 4"></TextBlock>
        </ComboBox>

И вот такой код к нему:

private void CustomIdeologyNameTextBox1_TextChanged(object sender, TextChangedEventArgs e)
        {
            try
            {
                ComboBoxCustomIdeology1.Text = CustomIdeologyNameTextBox1.Text;
            }
            catch(NullReferenceException)
            {
                ComboBoxCustomIdeology1.Text = "-";
            }
        }

        private void CustomIdeologyNameTextBox2_TextChanged(object sender, TextChangedEventArgs e)
        {
            try
            {
                ComboBoxCustomIdeology2.Text = CustomIdeologyNameTextBox2.Text;
            }
            catch
            {
                ComboBoxCustomIdeology2.Text = "-";
            }

        }

        private void CustomIdeologyNameTextBox3_TextChanged(object sender, TextChangedEventArgs e)
        {
            try
            {
                ComboBoxCustomIdeology3.Text = CustomIdeologyNameTextBox3.Text;
            }
            catch
            {
                ComboBoxCustomIdeology3.Text = "-";

            }
        }

        private void CustomIdeologyNameTextBox4_TextChanged(object sender, TextChangedEventArgs e)
        {
            try { 
                ComboBoxCustomIdeology4.Text = CustomIdeologyNameTextBox4.Text;
            }
            catch
            {
                ComboBoxCustomIdeology3.Text = "-";
            }
        }

Т.е. у четырёх последних вариантов в комбо боксе должен быть текст четырёх текст боксов. Но почему-то при компиляции выдаёт NullReferenceException. Блоки обработки не помогают - всё так же. Буду благодарен за помощь.