Fixed #25718 -- Made a JSONField lookup value of None match keys that have a null value.

docs/ref/contrib/postgres/fields.txt

@@ -544,7 +544,7 @@ name::
     ...         }],
     ...     },
     ... })
-    >>> Dog.objects.create(name='Meg', data={'breed': 'collie'})
+    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': None})
 
     >>> Dog.objects.filter(data__breed='collie')
     <QuerySet [<Dog: Meg>]>
@@ -566,6 +566,23 @@ the :lookup:`jsonfield.contains` lookup instead.
 If only one key or index is used, the SQL operator ``->`` is used. If multiple
 operators are used then the ``#>`` operator is used.
 
+To query for ``null`` in JSON data, use ``None`` as a value::
+
+    >>> Dog.objects.filter(data__owner=None)
+    <QuerySet [<Dog: Meg>]>
+
+To query for missing keys, use the ``isnull`` lookup::
+
+    >>> Dog.objects.create(name='Shep', data={'breed': 'collie'})
+    >>> Dog.objects.filter(data__owner__isnull=True)
+    <QuerySet [<Dog: Shep>]>
+
+.. versionchanged:: 2.1
+
+    In older versions, using ``None`` as a  lookup value matches objects that
+    don't have the key rather than objects that have the key with a ``None``
+    value.
+
 .. warning::
 
     Since any string could be a key in a JSON object, any lookup other than

docs/releases/2.1.txt

@@ -372,6 +372,10 @@ Miscellaneous
 * Since migrations are now loaded from ``.pyc`` files, you might need to delete
   them if you're working in a mixed Python 2 and Python 3 environment.
 
+* Using ``None`` as a :class:`~django.contrib.postgres.fields.JSONField` lookup
+  value now matches objects that have the specified key and a null value rather
+  than objects that don't have the key.
+
 .. _deprecated-features-2.1:
 
 Features deprecated in 2.1