Fixed #27582 -- Allowed HStoreField to store null values.

docs/ref/contrib/postgres/fields.txt

@@ -275,8 +275,9 @@ A more useful index is a ``GIN`` index, which you should create using a
 
 .. class:: HStoreField(**options)
 
-    A field for storing mappings of strings to strings. The Python data type
-    used is a ``dict``.
+    A field for storing key-value pairs. The Python data type used is a
+    ``dict``. Keys must be strings, and values may be either strings or nulls
+    (``None`` in Python).
 
     To use this field, you'll need to:
 
@@ -287,6 +288,10 @@ A more useful index is a ``GIN`` index, which you should create using a
     You'll see an error like ``can't adapt type 'dict'`` if you skip the first
     step, or ``type "hstore" does not exist`` if you skip the second.
 
+    .. versionchanged:: 1.11
+
+        Added the ability to store nulls. Previously, they were cast to strings.
+
 .. note::
 
     On occasions it may be useful to require or restrict the keys which are

docs/ref/contrib/postgres/forms.txt

@@ -144,8 +144,8 @@ Fields
 .. class:: HStoreField
 
     A field which accepts JSON encoded data for an
-    :class:`~django.contrib.postgres.fields.HStoreField`. It will cast all the
-    values to strings. It is represented by an HTML ``<textarea>``.
+    :class:`~django.contrib.postgres.fields.HStoreField`. It casts all values
+    (except nulls) to strings. It is represented by an HTML ``<textarea>``.
 
     .. admonition:: User friendly forms
 
@@ -159,6 +159,10 @@ Fields
         valid for a given field. This can be done using the
         :class:`~django.contrib.postgres.validators.KeysValidator`.
 
+    .. versionchanged:: 1.11
+
+        Added the ability to store nulls.
+
 ``JSONField``
 -------------