Index: db-api.txt
===================================================================
--- db-api.txt	(revision 3502)
+++ db-api.txt	(working copy)
@@ -578,6 +578,9 @@
     p = b.author         # Hits the database.
     c = p.hometown       # Hits the database.
 
+Note that ``select_related()`` will not follow foreign keys where
+``null=True`` is set.
+
 ``extra(select=None, where=None, params=None, tables=None)``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~