Clean up serialization on some fields

cms/xmodule_namespace.py

@@ -17,6 +17,9 @@ class DateTuple(ModelType):
         return datetime.datetime(*value[0:6])
 
     def to_json(self, value):
+        if value is None:
+            return None
+
         return list(value.timetuple())
 
 

common/lib/xmodule/xmodule/course_module.py

@@ -139,7 +139,7 @@ class TextbookList(ModelType):
         json_data = []
         for val in values:
             if isinstance(val, Textbook):
-                json_data.append((textbook.title, textbook.book_url))
+                json_data.append((val.title, val.book_url))
             elif isinstance(val, tuple):
                 json_data.append(val)
             else: