ArgumentNullException calling OpenSpecificEditor (worked in VS2010)

Hello.  I have a VSPackage that has a custom editor for non-file based item.  This has been working fine in VS2008 and VS2010.  I am attempting to upgrade my package to VS2012 and am getting this exception when trying to open the item.  The OpenItem code from my UIHierarchy is included below.

System.ArgumentNullException occurred
  HResult=-2147467261
  Message=Value cannot be null.
Parameter name: o
  ParamName=o
  Source=mscorlib
  StackTrace:
       at System.Runtime.InteropServices.Marshal.GetIUnknownForObjectNative(Object o, Boolean onlyInContext)
       at Microsoft.VisualStudio.PlatformUI.SafeIUnknown.FromObject(Object o)
  InnerException:

    Public Function OpenItem(ByVal itemid As UInteger, ByRef rguidLogicalView As System.Guid, ByVal punkDocDataExisting As System.IntPtr, _
                             ByRef ppWindowFrame As Microsoft.VisualStudio.Shell.Interop.IVsWindowFrame) As Integer Implements Microsoft.VisualStudio.Shell.Interop.IVsProject.OpenItem
        Debug.WriteLine("OpenItem")
        ppWindowFrame = Nothing
        If _nodesbyid.ContainsKey(itemid) Then
            Dim node = _nodesbyid(itemid)
            ' show the document, set ppWindowFrame
            CodeReviewToolsPackage.Instance.WaitCursor()
            Dim frame As IVsWindowFrame = GetDocumentWindowFrame(node)
            If (frame Is Nothing) Then
                Dim empty As Guid = Guid.Empty
                Dim flags As UInteger = (__VSOSEFLAGS.OSE_UseOpenWithDialog Or _VSRDTFLAGS.RDT_DontAddToMRU)  ' &H10010048
                Dim opendocument As IVsUIShellOpenDocument = CodeReviewToolsPackage.Instance.GetService(Of SVsUIShellOpenDocument, IVsUIShellOpenDocument)()
                ComUtils.ThrowOnFailure(opendocument.OpenSpecificEditor(flags, node.CanonicalName, _
                                        node.EditorGuid, Nothing, empty, node.Caption, DirectCast(Me, IVsUIHierarchy), node.ItemId, _
                                         punkDocDataExisting, DirectCast(CodeReviewToolsPackage.Instance, Microsoft.VisualStudio.OLE.Interop.IServiceProvider), frame))


                Dim docview As ICodeReviewToolsEditor
                ComUtils.ThrowOnFailure(frame.GetProperty(__VSFPROPID.VSFPROPID_DocView, docview))
                docview.WindowFrame = frame
                frame.Show()
                ppWindowFrame = frame
            Else
                frame.Hide() ' Make sure the activated event is thrown when we .Show()
                frame.Show()
                ppWindowFrame = frame
            End If

            Return VSConstants.S_OK
        Else
            Return VSConstants.E_FAIL
        End If
    End Function