Insert Integer Null Value

 Hi,
I have SQL Server DB, and I tried to insert some data. I used StorProc to do the insertion as follows:
ALTER PROCEDURE dbo.InsertPage
   
    (
    @PageID int,
    @ParID int,
    @ChiID int,
    @PageContent ntext
    )
AS   
    INSERT INTO MP_Page
                            (PageID, ParID, ChiID, PageContent)
      VALUES     (@PageID,@ParID,@ChiID,@PageContent)


    RETURN

The problem happened when I tired to insert int null value in field ChiID which is allow null and here is my code
private void InsertPage(PagesDB PageDB, out pagedetails pages)
        {
            if (txtChild.Text == "")
            {
                int varChildID;
                varChildID = int.Parse(txtChild.Text.Trim());
                pages = new pagedetails(int.Parse(ddlParent.SelectedValue.Trim()), varChildID,
                int.Parse(txtPageID.Text.Trim()), FTB.Text.Trim());
            }
            else
            {
                pages = new pagedetails(int.Parse(ddlParent.SelectedValue.Trim()), int.Parse(txtChild.Text.Trim()),
                int.Parse(txtPageID.Text.Trim()), FTB.Text.Trim());
            }
                PageDB.InsertPage(pages);
        }
 
the error message says Input string was not in a correct format.
Any idea ??
Thank you