If Assigning Cell Values in DataGridView to VbNull For a particular column it's showing 1

See more:

VB

.NET

DataGridView

I Am New to VB... For Learning Purpose am trying to Edit the Cell values in DataGridView... If cell values is nothing or empty am trying to show NULL... If am Using this code

Private Sub Btn_ShowAll_Click(sender As System.Object, e As System.EventArgs) Handles Btn_ShowAll.Click
       Dim da As New SqlDataAdapter("Select * From Tablexy", con)
       Dim ds As New DataTable("Tablexy")
       Dim dgr As DataGridViewRow
       con.Open()
       da.Fill(ds)
       Dgv1.DataSource = ds
       con.Close()
       For r As Int32 = 0 To Dgv1.Rows.Count - 2
           dgr = Dgv1.Rows(r)
           For i As Int32 = 0 To dgr.Cells.Count - 2
               If Convert.ToString(dgr.Cells(i).Value) = "" Then
                   dgr.Cells(i).Value = vbNull
               End If
           Next
       Next

   End Sub

But For One Column OrderingCost The Values are showing as 1 even though they are null values...

Columns in Tablexy
Product (Pk,Nvarchar(50) NotNull),ProductDesc(Nvarchar(50),Null), ProductType(Nvarchar(50),Null),Holdingcost (Real, NotNull),OrderingCost(Real,Null).

Why is OrderingCost shown as 1.... Any Explanation Will be Helpful....