Index: sqlobject/col.py
===================================================================
--- sqlobject/col.py	(revision 2682)
+++ sqlobject/col.py	(working copy)
@@ -980,6 +980,8 @@
     def to_python(self, value, state):
         if value in self.enumValues:
             return value
+        elif not self.notNone and value is None:
+            return None
         else:
             raise validators.Invalid("expected a member of %r in the EnumCol '%s', got %r instead" % \
                                      (self.enumValues, self.name, value), value, state)