[WPF] Formatowanie TextBoxa w behind-code

        <Grid Grid.Column="0" Background="#FF85B959" Margin="0,0,0,0">
            <Image  Name="Logo_0_0"  HorizontalAlignment="Center" VerticalAlignment="Center"></Image>
            <Image  Name="Stan_0_0"  HorizontalAlignment="Left" VerticalAlignment="Top" Stretch="None" ></Image>
            <TextBox Name="TBNo_0_0"  Background="#FF85B959"  FontFamily="Times New Roman" />
            <Image  Name="Pilka_0_0"  HorizontalAlignment="Left" VerticalAlignment="Bottom" Stretch="None" ></Image>
        </Grid>
        <Grid Grid.Column="1" Background="#FF85B959" Margin="0,0,0,1">
            <Image  Name="Logo_0_1"  HorizontalAlignment="Center" VerticalAlignment="Center"></Image>
            <Image  Name="Stan_0_1"  HorizontalAlignment="Left" VerticalAlignment="Top" Stretch="None" ></Image>
            <TextBox Name="TBNo_0_1"  Background="#FF85B959" FontFamily="Times New Roman" />
            <Image  Name="Pilka_0_1"  HorizontalAlignment="Left" VerticalAlignment="Bottom" Stretch="None" ></Image>
        </Grid>
        <Grid Grid.Column="2" Background="#FF85B959" Margin="0,0,0,1">
            <Image  Name="Logo_0_2"  HorizontalAlignment="Center" VerticalAlignment="Center"></Image>
            <Image  Name="Stan_0_2"  HorizontalAlignment="Left" VerticalAlignment="Top" Stretch="None" ></Image>
            <TextBox Name="TBNo_0_2"  Background="#FF85B959"  FontFamily="Times New Roman" />
            <Image  Name="Pilka_0_2"  HorizontalAlignment="Left" VerticalAlignment="Bottom" Stretch="None" ></Image>
        </Grid>

       public MainWindow()
        {
            InitializeComponent();

            TBNo_0_0 = StylTekstu(0, 0);
            TBNo_0_1 = StylTekstu(0, 1);
            TBNo_0_2 = StylTekstu(0, 2);
   
        }

        TextBox[,] txtBox = new TextBox[0, 3];

        public TextBox StylTekstu(int i, int j)

        {
            txtBox[i, j].Text = "6";     // tutaj wyskakuje bład : System.NullReferenceException: „Odwołanie do obiektu nie zostało ustawione na wystąpienie obiektu.”

            txtBox[i, j].FontSize = 13;
            txtBox[i, j].FontWeight = FontWeights.Bold;
            txtBox[i, j].Foreground = Brushes.Red;
            txtBox[i, j].VerticalAlignment = VerticalAlignment.Center;
            txtBox[i, j].HorizontalAlignment = HorizontalAlignment.Center;
            txtBox[i, j].TextAlignment = TextAlignment.Center;
            txtBox[i, j].BorderBrush = Brushes.White;

            return txtBox[i, j];
        }

 TBNo_0_0 = StylTekstu(0, 0)