diff --git a/django/core/serializers/base.py b/django/core/serializers/base.py
index e939c0c6e7..fb293c7c13 100644
--- a/django/core/serializers/base.py
+++ b/django/core/serializers/base.py
@@ -11,7 +11,7 @@ from django.db import models
 class SerializationError(Exception):
     """Something bad happened during serialization."""
     pass
-    
+
 class DeserializationError(Exception):
     """Something bad happened during deserialization."""
     pass
@@ -20,15 +20,15 @@ class Serializer(object):
     """
     Abstract serializer base class.
     """
-    
+
     def serialize(self, queryset, **options):
         """
         Serialize a queryset.
         """
         self.options = options
-        
+
         self.stream = options.get("stream", StringIO())
-        
+
         self.start_serialization()
         for obj in queryset:
             self.start_object(obj)
@@ -44,61 +44,65 @@ class Serializer(object):
             self.end_object(obj)
         self.end_serialization()
         return self.getvalue()
-    
+
     def get_string_value(self, obj, field):
         """
         Convert a field's value to a string.
         """
         if isinstance(field, models.DateTimeField):
-            value = getattr(obj, field.name).strftime("%Y-%m-%d %H:%M:%S")
+            value = getattr(obj, field.name)
+            if value is None:
+                value = ''
+            else:
+                value = value.strftime("%Y-%m-%d %H:%M:%S")
         elif isinstance(field, models.FileField):
             value = getattr(obj, "get_%s_url" % field.name, lambda: None)()
         else:
             value = field.flatten_data(follow=None, obj=obj).get(field.name, "")
         return str(value)
-    
+
     def start_serialization(self):
         """
         Called when serializing of the queryset starts.
         """
         raise NotImplementedError
-    
+
     def end_serialization(self):
         """
         Called when serializing of the queryset ends.
         """
         pass
-    
+
     def start_object(self, obj):
         """
         Called when serializing of an object starts.
         """
         raise NotImplementedError
-    
+
     def end_object(self, obj):
         """
         Called when serializing of an object ends.
         """
         pass
-    
+
     def handle_field(self, obj, field):
         """
         Called to handle each individual (non-relational) field on an object.
         """
         raise NotImplementedError
-    
+
     def handle_fk_field(self, obj, field):
         """
         Called to handle a ForeignKey field.
         """
         raise NotImplementedError
-    
+
     def handle_m2m_field(self, obj, field):
         """
         Called to handle a ManyToManyField.
         """
         raise NotImplementedError
-    
+
     def getvalue(self):
         """
         Return the fully serialized queryset.
@@ -109,7 +113,7 @@ class Deserializer(object):
     """
     Abstract base deserializer class.
     """
-    
+
     def __init__(self, stream_or_string, **options):
         """
         Init this serializer given a stream or a string
@@ -123,39 +127,39 @@ class Deserializer(object):
         # deserialization starts (otherwise subclass calls to get_model()
         # and friends might fail...)
         models.get_apps()
-    
+
     def __iter__(self):
         return self
-    
+
     def next(self):
         """Iteration iterface -- return the next item in the stream"""
         raise NotImplementedError
-        
+
 class DeserializedObject(object):
     """
     A deserialzed model.
-    
+
     Basically a container for holding the pre-saved deserialized data along
     with the many-to-many data saved with the object.
-    
+
     Call ``save()`` to save the object (with the many-to-many data) to the
     database; call ``save(save_m2m=False)`` to save just the object fields
     (and not touch the many-to-many stuff.)
     """
-    
+
     def __init__(self, obj, m2m_data=None):
         self.object = obj
         self.m2m_data = m2m_data
-        
+
     def __repr__(self):
         return "<DeserializedObject: %s>" % str(self.object)
-        
+
     def save(self, save_m2m=True):
         self.object.save()
         if self.m2m_data and save_m2m:
             for accessor_name, object_list in self.m2m_data.items():
                 setattr(self.object, accessor_name, object_list)
-        
-        # prevent a second (possibly accidental) call to save() from saving 
+
+        # prevent a second (possibly accidental) call to save() from saving
         # the m2m data twice.
         self.m2m_data = None