reverted previous patch

VERSION

@@ -1 +1 @@
-Version 2.6.0-development+timestamp.2013.09.06.16.28.32
+Version 2.6.0-development+timestamp.2013.09.07.21.00.37

gluon/validators.py

@@ -2341,7 +2341,7 @@ class IS_DATETIME(Validator):
             return (ovalue, translate(self.error_message) % self.extremes)
 
     def formatter(self, value):
-        if value is None or value == '':
+        if value is None:
             return None
         format = self.format
         year = value.year