C# Richtextbox w TabControl

        private void newModuleToolStripMenuItem_Click(object sender, EventArgs e)
        {
            TabPage tab = new TabPage();
            RichTextBox textbox = new RichTextBox();

            tab.Text = promptValue;
            tabControl1.Controls.Add(tab);
            tabControl1.SelectTab(tabControl1.TabCount - 1);

            textbox.Parent = tabControl1.SelectedTab;
            textbox.Dock = DockStyle.Fill;
        }

    private void saveModuleToolStripMenuItem_Click(object sender, EventArgs e)
        {
            string name = tabControl1.TabPages[0].Text;
            RichTextBox richText = tabControl1.SelectedTab.Controls[0] as RichTextBox;

            if (richText != null)
            {
                saveFileDialog1.Filter = ("TXT file|*.txt");
                saveFileDialog1.FileName = name;
                saveFileDialog1.ShowDialog();
                File.WriteAllLines(saveFileDialog1.FileName, richText.Lines); << Tu zgłasza że ruchText jest null.
            }
            else
            {
                MessageBox.Show("Null: " + '"' +  name + '"' + " is empty.");
            }
            
        }