xpath

Callstack:
    at User:SteveB/Sandbox/xpath
    at wiki.tree

System.ArgumentNullException: Argument cannot be null.
Parameter name: source
  at System.Linq.Check.Source (System.Object source) [0x00000] in <filename unknown>:0 
  at System.Linq.Enumerable.ToArray[PageBE] (IEnumerable`1 source) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.Logic.PageSiteMapBL.BuildHtmlSiteMap (MindTouch.Deki.Data.PageBE rootPage, System.String language, Int32 depth, Boolean reverse) [0x00000] in <filename unknown>:0 
  at MindTouch.Deki.DekiWikiService.WikiTree (System.String path, Nullable`1 depth, Nullable`1 reverse) [0x00000] in <filename unknown>:0 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0