Fixed to handle null (empty or None) specifications.

src/ZODB/UndoLogCompatible.py

@@ -88,11 +88,13 @@
 class UndoLogCompatible:
 
     def undoInfo(self, first, last, specification):
+        if specification:
             def filter(desc, spec=specification.items()):
                 get=desc.get
                 for k, v in spec:
                     if get(k, None) != v:
                         return 0
                 return 1
+        else: filter=None
             
         return self.undoLog(first, last, filter)