Index: django/forms/fields.py
===================================================================
--- django/forms/fields.py	(revision 9524)
+++ django/forms/fields.py	(working copy)
@@ -44,7 +44,7 @@
 )
 
 # These values, if given to to_python(), will trigger the self.required check.
-EMPTY_VALUES = (None, '')
+EMPTY_VALUES = (None, '', [], {}, (), set([]))
 
 
 class Field(object):