C# - Loop Through All Controls On Webpage

I need to loop through all the controls in my asp.net webpage and do something to the control. In one instance I'm making a giant string out of the page and emailing it to myself, and in another case I'm saving everything to a cookie. The problem is masterpages and items with collections of controls inside them. I want to be able to pass in a Page to the method, then have that method be generic enough to loop through all controls in the inner-most content page and work with them. I've tried doing this with recursion, but my recursion is incomplete. I want to pass a Page object into a method, and have that method loop through all controls in the innermost content page. How can I achieve this?

private static String controlToString(Control control)
{
StringBuilder result = new StringBuilder();
String controlID = String.Empty;
Type type = null;
foreach (Control c in control.Controls)
{
try
{
controlID = c.ID.ToString();
if (c is IEditableTextControl)
{
result.Append(controlID + ": " + ((IEditableTextControl)c).Text);
result.Append("<br />");
}
else if (c is ICheckBoxControl)
{
result.Append(controlID + ": " + ((ICheckBoxControl)c).Checked);
result.Append("<br />");
}
else if (c is ListControl)
{
result.Append(controlID + ": " + ((ListControl)c).SelectedValue);
result.Append("<br />");
}
else if (c.HasControls())
{
result.Append(controlToString(c));
}
//result.Append("<br />");
}
catch (Exception e)
{
}
}
return result.ToString();
}
Without Try/catch
Object reference not set to an instance of an object.
On line controlID = .....