Treeview control error GetImageUrl

[lumazi]

Everyone,

I'm having some trouble creating a treeview control in code. Here
is the block of code I'm workign with ...

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protected override void Render(System.Web.UI.HtmlTextWriter
writer)
{
try
{
TreeView sitesTree = new TreeView();
TreeNode newNode;
SPSite website = new SPSite("http://" +
System.Web.HttpContext.Current.Request.ServerVariables["HTTP_HOST"].ToString());
SPWeb web = website.OpenWeb();

sitesTree.SkipLinkText = "";
sitesTree.CollapseImageUrl = "";
sitesTree.ExpandImageUrl = "";
sitesTree.NoExpandImageUrl = "";
sitesTree.ShowExpandCollapse = true;
sitesTree.ImageSet = TreeViewImageSet.Simple;

foreach (SPWeb currentWeb in web.Webs)
{
newNode = new TreeNode();
newNode.ImageUrl = "";
newNode.Text = currentWeb.Title;
newNode.Value = currentWeb.Url;
sitesTree.Nodes.Add(newNode);
}
sitesTree.RenderControl(writer);
}
catch (Exception ex)
{
writer.Write(ex.Message + "<hr>");
writer.Write(ex.StackTrace + "<hr>");
}
}
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When I run the code I get the following error message ...

Object reference not set to an instance of an object.
---------------------------------------------------------------------------------------------------------------------------------------
at System.Web.UI.WebControls.TreeView.GetImageUrl(Int32 index) at
System.Web.UI.WebControls.TreeNode.Render(HtmlTextWriter writer, Int32
position, Boolean[] isLast, Boolean enabled) at
System.Web.UI.WebControls.TreeView.RenderContents(HtmlTextWriter
writer) at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer) at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter) at
System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter) at
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) at
MOSS2007WebPart.SimpleWebPart.Render(HtmlTextWriter writer) in C:\VS
Projects\MOSS2007WebPart\MOSS2007WebPart\Class1.cs:line 55
---------------------------------------------------------------------------------------------------------------------------------------

I've tried setting all of the image URL's but to no avail. Has anyone
run across this and have you found a solution?

Thank you for your help,

Scott Vercuski
(e-mail address removed)