Fixed #24844 -- Corrected has_changed implementation for HStoreField.

Backport of 43b2d88a5b from master

django/contrib/postgres/forms/hstore.py

@@ -34,3 +34,13 @@ class HStoreField(forms.CharField):
         for key, val in value.items():
             value[key] = six.text_type(val)
         return value
+
+    def has_changed(self, initial, data):
+        """
+        Return True if data differs from initial.
+        """
+        # For purposes of seeing whether something has changed, None is
+        # the same as an empty dict, if the data or initial value we get
+        # is None, replace it w/ {}.
+        initial_value = self.to_python(initial)
+        return super(forms.HStoreField, self).has_changed(initial_value, data)

docs/releases/1.8.3.txt

@@ -15,5 +15,7 @@ Bugfixes
 * Fixed crash during :djadmin:`makemigrations` if a migrations module either
   is missing ``__init__.py`` or is a file (:ticket:`24848`).
 
-* Fixed ``exists()`` returning incorrect results after annotation with
+* Fixed ``QuerySet.exists()`` returning incorrect results after annotation with
   ``Count()`` (:ticket:`24835`).
+
+* Corrected ``HStoreField.has_changed()`` (:ticket:`24844`).

tests/postgres_tests/test_hstore.py

@@ -4,6 +4,7 @@ from django.contrib.postgres import forms
 from django.contrib.postgres.fields import HStoreField
 from django.contrib.postgres.validators import KeysValidator
 from django.core import exceptions, serializers
+from django.forms import Form
 from django.test import TestCase
 
 from .models import HStoreModel
@@ -174,6 +175,12 @@ class TestFormField(TestCase):
         form_field = model_field.formfield()
         self.assertIsInstance(form_field, forms.HStoreField)
 
+    def test_empty_field_has_not_changed(self):
+        class HStoreFormTest(Form):
+            f1 = HStoreField()
+        form_w_hstore = HStoreFormTest()
+        self.assertFalse(form_w_hstore.has_changed())
+
 
 class TestValidator(TestCase):