cannot access empty field in gridview

[Mich]

Hi,

i made a gridview connected to a sql server db and i need to test the value
of a field of the gridview..
The problem is that field can be empty (e.g. when the content of that field
was previously deleted by another query) or NULL.

Now, when i try to access a record where that field has content, no problem,
but if it's empty or NULL, i get the error:
"Object reference not set to an instance of an object"

Any way to avoid that error?
Thanks
Mich

Protected Sub GridView1_RowDeleting(ByVal sender As Object, ByVal e As
System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles
GridView1.RowDeleting
Dim st1 As String
st1 = e.Values.Item("myfield").ToString
....