[library-web] mallard: do not fail on $(NULL)

[Frederic Peters <fpeters src gnome org>]

commit 69b51fdfd5a8b84c5038f41eef4c1fc091bf4553
Author: Frédéric Péters <fpeters 0d be>
Date:   Sun Jun 23 16:02:05 2013 +0200

    mallard: do not fail on $(NULL)

 src/modtypes/mallard.py |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/modtypes/mallard.py b/src/modtypes/mallard.py
index efa00d2..2cc43c3 100644
--- a/src/modtypes/mallard.py
+++ b/src/modtypes/mallard.py
@@ -287,6 +287,9 @@ class MallardModule(DocModule):
             mallard_cache = MallardCache()
             for doc_page in doc_pages:
                 xml_file = os.path.join(lang_dirname, doc_page)
+                if doc_page == '$(NULL)':
+                    doc_pages.remove(doc_page)
+                    continue
                 if not os.path.exists(xml_file):
                     if lang in doc.languages:
                         doc.languages.remove(lang)