I have a text box and datetime where can i enter an integer . I wish to store this in a SQL Server Database. If i enter then I would store a NULL. However if the text box is left blank, I get an error Input string was not in a correct format. How can I work around this, and get the null into the db?

this Code in method

Code:
public void Add_ItemSeasonalPrices(string ItemCode, DateTime FromDate, DateTime ToDate, decimal WholeSaleForFirstUnit,
...