diff -r 49be8619b745 -r 328542c4fdc8 migration.py
--- a/migration.py	Wed Jun 29 18:27:01 2011 +0200
+++ b/migration.py	Wed Jun 29 18:28:36 2011 +0200
@@ -509,6 +509,8 @@
                         if version_strictly_lower(version, ver):
                             version = ver
                             source = src
+                    elif op == None:
+                        continue
                     else:
                         print 'unable to handle this case', oper, version, op, ver
             # "solve" constraint satisfaction problem