Int field in winform does not update null values in SQL server database using C#

In my Winforms C# application, I have fields with Int data type and they are set to accept null values in SQL Server database (allow nulls).

In the forms I have some textboxes which are bound to those int data type fields. If I don't enter anything while creating a new record, it accepts and saves record in sql database. If I enter a number in the textbox, it also accepts it, and then if I delete the number, it doesn't allow me to move to the next field.

If I set its value as null or "" through code, it is not updated in database and even does not update changes which I made in other non int text fields (this update works fine if I dont touch int fields).
 
I am using following to enter null in this field.

IDTextBox.Text = "";
IDTextBox.Text = null;

On Form Load event, I have following code.

this.itemsTableAdapter.Fill(this.sBSDBDataSet.Items);

I am using following code to save new record in database

this.itemsbindingSource.AddNew();
this.Validate();
this.itemsbindingSource.EndEdit();
this.tableAdapterManager.UpdateAll(this.sBSDBDataSet);

On this form there are many fields in which I enter data and then press UPDATE button to update the record in SQL Server database. I am using following method to update the record

this.Validate();
this.itemsbindingSource.EndEdit();
this.tableAdapterManager.UpdateAll(this.sBSDBDataSet);

All other fields seem to work fine except the fields having int datatype (although in sql table I have allowed them to be null).
.

As I mentioned above, int field text box on WinForm does not even allow to move to next field during data entry if we do not enter something in it

What can I do for the textbox accept null values?