Check DataGridView cell is empty or has value 0 using C# and VB.Net

Dear Sir 

I'm trying to check a cell that is empty and has a value of 0 then cannot addnew row from bindingsource to datagridview with method ProcessCmd 

but below code only for empty and column edit or not readonly productname position cell (1) dan Qty position cell (5).

Please Guide me

Thanks

Protected Overrides Function ProcessCmdKey(ByRef msg As Message, ByVal keyData As Keys) As Boolean
    If keyData = Keys.Tab AndAlso CBool(Keys.Enter) Then
        Dim SelectDgv = GetSELECT()
        If Me.Datagridview1.Rows.Count > 0 Then
            If Not Datagridview1.CurrentRow.Cells.Cast(Of DataGridViewCell).Any(Function(cell) String.IsNullOrEmpty(cell.FormattedValue?.ToString())) Then
                BindingSource1.AddNew()
            Else
                Datagridview1.CurrentCell = Datagridview1.CurrentRow.Cells("PRODUCTNAME")
                Datagridview1.BeginEdit(False)
            End If
        Else
        End If
        Return True
        ElseIf keyData = Keys.F1 AndAlso CBool(Keys.Enter) Then
            Datagridview1.CurrentCell = Datagridview1.CurrentRow.Cells("QTY")
            Datagridview1.BeginEdit(False)
        Else
    End If
    Return MyBase.ProcessCmdKey(msg, keyData)
End Function