Fixed #5102 -- Fixed model saving so that 0 can be used as a primary key value. Thanks, oggie rob.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@5933 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/base.py

@@ -209,7 +209,7 @@ class Model(object):
 
         # First, try an UPDATE. If that doesn't update anything, do an INSERT.
         pk_val = self._get_pk_val()
-        pk_set = bool(pk_val)
+        pk_set = pk_val is not None
         record_exists = True
         if pk_set:
             # Determine whether a record with the primary key already exists.