仅当LiteralControl尚未分配文本时，如何才能覆盖LiteralControl的文本？

This code:

private void btnSave_Click(object sender, EventArgs e)
{
    LiteralControl message = null;
    try
    {
        message = new LiteralControl();
        Controls.Add(message);
        ConditionallyCreateList();
        SaveInputToList();
        List<ListColumns> listOfListItems = ReadFromList();
        GeneratePDF(listOfListItems); // using iTextSharp
    }
    catch (Exception ex)
    {
        message.Text = String.Format("Exception occurred: {0}", ex.Message);
    }
    if (message.Text.Length <= 1)
    {
        message.Text = "Saving the data and converting it to a PDF has been successful";
    }
}
private void btnSave_Click(object