migrator.py : IDmapper ignore empty values

server/web2py/applications/vidjil/scripts/migrator.py

@@ -78,6 +78,8 @@ class IdMapper():
         self.mapping = {}
 
     def getMatchingId(self, oid):
+        if oid is None:
+            return oid
         if oid not in self.mapping:
             self.log.debug('id %d not in mapping, returning it' % oid)
             self.log.debug("mapping: " + str(self.mapping.keys()))