\constfunc{wxString}{GetFilename}{\void}
-Gets the filename associated with this document, or NULL if none is
+Gets the filename associated with this document, or "" if none is
associated.
\membersection{wxDocument::GetFirstView}
\func{virtual bool}{OnOpenDocument}{\param{const wxString\& }{filename}}
-Constructs an input file stream for the given filename (which must not be NULL),
+Constructs an input file stream for the given filename (which must not be empty),
and calls LoadObject. If LoadObject returns TRUE, the document is set to
unmodified; otherwise, an error message box is displayed. The document's
views are notified that the filename has changed, to give windows an opportunity
\func{virtual bool}{OnSaveDocument}{\param{const wxString\& }{filename}}
-Constructs an output file stream for the given filename (which must not be NULL),
+Constructs an output file stream for the given filename (which must not be empty),
and calls SaveObject. If SaveObject returns TRUE, the document is set to
unmodified; otherwise, an error message box is displayed.