Fix cache enrollments of None.

LEARNER-5001

ecommerce/programs/conditions.py

@@ -20,6 +20,9 @@ Condition = get_model('offer', 'Condition')
 logger = logging.getLogger(__name__)
 
 
+CACHE_MISS = object()
+
+
 class ProgramCourseRunSeatsCondition(SingleItemConsumptionConditionMixin, Condition):
     class Meta(object):
         app_label = 'programs'
@@ -52,8 +55,9 @@ class ProgramCourseRunSeatsCondition(SingleItemConsumptionConditionMixin, Condit
             resource=resource_name,
             username=basket.owner.username,
         )
-        data_list = cache.get(cache_key)
-        if not data_list:
+        data_list = cache.get(cache_key, CACHE_MISS)
+        if data_list is CACHE_MISS:
+            data_list = None
             user = basket.owner.username
             try:
                 if waffle.switch_is_active("debug_logging_for_excessive_lms_calls"):

ecommerce/programs/tests/test_conditions.py

@@ -22,7 +22,7 @@ class ProgramCourseRunSeatsConditionTests(ProgramTestMixin, TestCase):
     def setUp(self):
         super(ProgramCourseRunSeatsConditionTests, self).setUp()
         self.condition = factories.ProgramCourseRunSeatsConditionFactory()
-        self.test_product = ProductFactory(stockrecords__price_excl_tax=10)
+        self.test_product = ProductFactory(stockrecords__price_excl_tax=10, categories=[])
         self.site.siteconfiguration.enable_partial_program = True
 
     def test_name(self):
@@ -266,3 +266,25 @@ class ProgramCourseRunSeatsConditionTests(ProgramTestMixin, TestCase):
         with mock.patch('ecommerce.programs.conditions.traverse_pagination') as mock_processing_entitlements:
             self.assertFalse(self.condition.is_satisfied(offer, basket))
             mock_processing_entitlements.assert_not_called()
+
+    @httpretty.activate
+    def test_get_lms_resource_for_user_caching_none(self):
+        """
+        LMS resource should be properly cached when enrollments is None.
+        """
+        basket = factories.BasketFactory(site=self.site, owner=factories.UserFactory())
+        resource_name = 'test_resource_name'
+        mock_endpoint = mock.Mock()
+        mock_endpoint.get.return_value = None
+
+        return_value = self.condition._get_lms_resource_for_user(basket, resource_name, mock_endpoint)  # pylint: disable=protected-access
+
+        self.assertEqual(return_value, [])
+        self.assertEquals(mock_endpoint.get.call_count, 1, 'Endpoint should be called before caching.')
+
+        mock_endpoint.reset_mock()
+
+        return_value = self.condition._get_lms_resource_for_user(basket, resource_name, mock_endpoint)  # pylint: disable=protected-access
+
+        self.assertEqual(return_value, [])
+        self.assertEquals(mock_endpoint.get.call_count, 0, 'Endpoint should NOT be called after caching.')