diff --git a/studentrecord/mapping.py b/studentrecord/mapping.py
index 7ad8fa1..f7b88bf 100644
--- a/studentrecord/mapping.py
+++ b/studentrecord/mapping.py
@@ -82,6 +82,8 @@ def _build_str(row, name, o):
             o = True
         elif o in ('false', 'False'):
             o = False
+        elif o in ('null', 'none', 'None'):
+            o = None
         return o
 
     _build_unicode = _build_str