compat for django 1.3x fixed

empty was introduced Django > 1.3

rest_framework/compat.py

@@ -343,6 +343,13 @@ except ImportError:
             kw = dict((k, int(v)) for k, v in kw.iteritems() if v is not None)
             return datetime.datetime(**kw)
 
+
+# empty does not exist in 1.3x
+if django.VERSION >= (1, 4):
+    from django.utils.functional import empty
+else:
+    empty = object()
+
 # Markdown is optional
 try:
     import markdown

rest_framework/serializers.py

@@ -5,9 +5,8 @@ from decimal import Decimal
 from django.db import models
 from django.forms import widgets
 from django.utils.datastructures import SortedDict
-from django.utils.functional import empty
 from django.core.exceptions import ImproperlyConfigured
-from rest_framework.compat import get_concrete_model
+from rest_framework.compat import get_concrete_model, empty
 
 # Note: We do the following so that users of the framework can use this style:
 #