Generate TypeError if from or to_json fail.

common/lib/xmodule/xmodule/fields.py

@@ -58,8 +58,7 @@ class Date(ModelType):
         else:
             msg = "Field {0} has bad value '{1}'".format(
                 self._name, field)
-            log.warning(msg)
-            return None
+            raise TypeError(msg)
 
     def to_json(self, value):
         """
@@ -76,6 +75,8 @@ class Date(ModelType):
                 return value.strftime('%Y-%m-%dT%H:%M:%SZ')
             else:
                 return value.isoformat()
+        else:
+            raise TypeError("Cannot convert {} to json".format(value))
 
 TIMEDELTA_REGEX = re.compile(r'^((?P<days>\d+?) day(?:s?))?(\s)?((?P<hours>\d+?) hour(?:s?))?(\s)?((?P<minutes>\d+?) minute(?:s)?)?(\s)?((?P<seconds>\d+?) second(?:s)?)?$')
 

common/lib/xmodule/xmodule/tests/test_fields.py

@@ -44,7 +44,8 @@ class DateTest(unittest.TestCase):
     def test_return_None(self):
         self.assertIsNone(DateTest.date.from_json(""))
         self.assertIsNone(DateTest.date.from_json(None))
-        self.assertIsNone(DateTest.date.from_json(['unknown value']))
+        with self.assertRaises(TypeError):
+            DateTest.date.from_json(['unknown value'])
 
     def test_old_due_date_format(self):
         current = datetime.datetime.today()
@@ -83,6 +84,8 @@ class DateTest(unittest.TestCase):
             DateTest.date.to_json(
                 DateTest.date.from_json("2012-12-31T23:00:01-01:00")),
             "2012-12-31T23:00:01-01:00")
+        with self.assertRaises(TypeError):
+            DateTest.date.to_json('2012-12-31T23:00:01-01:00')
 
 
 class TimedeltaTest(unittest.TestCase):