Tolerate null on Json db load

A icehouse->juno migration issue has surfaced where
resource.properties_data is null for existing resource records.

This change fixes the Json db type to treat None the same as
the serialized JSON 'null'.

Change-Id: Ia0b9a23a7798c95fbbcba439ffb8203b50367e7c
Closes-Bug: #1383505

heat/db/sqlalchemy/types.py

@@ -34,6 +34,8 @@ def process_bind_param(self, value, dialect):
         return dumps(value)
 
     def process_result_value(self, value, dialect):
+        if value is None:
+            return None
         return loads(value)
 
 

heat/tests/test_sqlalchemy_types.py

@@ -47,8 +47,20 @@ def test_process_bind_param(self):
         result = self.sqltype.process_bind_param(value, dialect)
         self.assertEqual('{"foo": "bar"}', result)
 
+    def test_process_bind_param_null(self):
+        dialect = None
+        value = None
+        result = self.sqltype.process_bind_param(value, dialect)
+        self.assertEqual('null', result)
+
     def test_process_result_value(self):
         dialect = None
         value = '{"foo": "bar"}'
         result = self.sqltype.process_result_value(value, dialect)
         self.assertEqual({'foo': 'bar'}, result)
+
+    def test_process_result_value_null(self):
+        dialect = None
+        value = None
+        result = self.sqltype.process_result_value(value, dialect)
+        self.assertIsNone(result)