title: Catch exception for null value in a DataTable
body: <p>I have an application in C# (winforms) that uses code generated by wizards for database management (datasets, datatables, etc.). If for example I have a datacolumn configured to allow null values (property AllowDBNull = true) and when a null value is entered (in a form) is configured to throw an exception (property NullValue = ThrowException). When in a form a textfield is edited and left blank it won't let the user switch focus to another control, I think it might be because of the NullValue property to throw an exception).The question is: how can I catch the exception and set a proper value.</p>