1 files changed, 27 insertions, 22 deletions
diff --git a/django/db/models/query.py b/django/db/models/query.py
index f16e6869e3..3aa1241d1a 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -727,30 +727,35 @@ def parse_lookup(kwarg_items, opts):
     joins, where, params = SortedDict(), [], []
 
     for kwarg, value in kwarg_items:
-        if value is not None:
-            path = kwarg.split(LOOKUP_SEPARATOR)
-            # Extract the last elements of the kwarg.
-            # The very-last is the lookup_type (equals, like, etc).
-            # The second-last is the table column on which the lookup_type is
-            # to be performed. If this name is 'pk', it will be substituted with
-            # the name of the primary key.
-            # If there is only one part, or the last part is not a query
-            # term, assume that the query is an __exact
-            lookup_type = path.pop()
-            if lookup_type == 'pk':
-                lookup_type = 'exact'
-                path.append(None)
-            elif len(path) == 0 or lookup_type not in QUERY_TERMS:
-                path.append(lookup_type)
-                lookup_type = 'exact'
+        path = kwarg.split(LOOKUP_SEPARATOR)
+        # Extract the last elements of the kwarg.
+        # The very-last is the lookup_type (equals, like, etc).
+        # The second-last is the table column on which the lookup_type is
+        # to be performed. If this name is 'pk', it will be substituted with
+        # the name of the primary key.
+        # If there is only one part, or the last part is not a query
+        # term, assume that the query is an __exact
+        lookup_type = path.pop()
+        if lookup_type == 'pk':
+            lookup_type = 'exact'
+            path.append(None)
+        elif len(path) == 0 or lookup_type not in QUERY_TERMS:
+            path.append(lookup_type)
+            lookup_type = 'exact'
 
-            if len(path) < 1:
-                raise TypeError, "Cannot parse keyword query %r" % kwarg
+        if len(path) < 1:
+            raise TypeError, "Cannot parse keyword query %r" % kwarg
+        
+        if value is None:
+            # Interpret '__exact=None' as the sql '= NULL'; otherwise, reject
+            # all uses of None as a query value.
+            if lookup_type != 'exact':
+                raise ValueError, "Cannot use None as a query value"
 
-            joins2, where2, params2 = lookup_inner(path, lookup_type, value, opts, opts.db_table, None)
-            joins.update(joins2)
-            where.extend(where2)
-            params.extend(params2)
+        joins2, where2, params2 = lookup_inner(path, lookup_type, value, opts, opts.db_table, None)
+        joins.update(joins2)
+        where.extend(where2)
+        params.extend(params2)
     return joins, where, params
 
 class FieldFound(Exception):