CommandControl.xaml.cs

private async void CommandTextBox_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Return)
    {
        var textBox = (TextBox)sender;

        if (string.IsNullOrWhiteSpace(textBox.Text))
        {
            return;
        }

        var command = textBox.Text;

        textBox.Text = string.Empty;

        await ExecuteCommand(command);
    }
}