how do i get a value from the data item in my datagrid

I am trying to get at information that was passed into my datagrid via a datareader.
When the datagrid is set into edit mode and a button is pressed within my datagrid

Private Sub departmentsGrid_ItemCommand(ByVal source As Object, ByVal e As System.Web.UI.WebControls.DataGridCommandEventArgs) Handles departmentsGrid.ItemCommand
        Select Case e.CommandName
            Case "btnUploadFile_Click"
       
                Dim departmentID As String = e.Item.DataItem("DepartmentID").ToString

            End Select
    End Sub
End Class

This says

 System.NullReferenceException: Object variable or With block variable not set.

Im not sure how to get at information in my datagrid.

i have also tried

DataBinder.Eval(Container.DataItem, "ImagePath")

Same thing happens