Fixed compilation error for Motif.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@34762 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/notebook.cpp

@@ -304,7 +304,7 @@ bool wxNotebook::RemovePage(size_t nPage)
 // remove one page from the notebook
 wxWindow* wxNotebook::DoRemovePage(size_t nPage)
 {
-    wxCHECK( IS_VALID_PAGE(nPage), false );
+    wxCHECK( IS_VALID_PAGE(nPage), NULL );
 
     m_pages[nPage]->Show(false);
     //    m_pages[nPage]->Lower();