Improve docstring

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28483 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/interfaces/cache_plugin.py

@@ -57,7 +57,7 @@ class ICachePlugin(Interface):
   def get(cache_id, scope, default=None):
     """get the calculated value according to the cache_id and scope.
     raise KeyError if key does not exists and no default value provided.
-    return CacheEntry
+    return CacheEntry or default
     """
 
   def set(cache_id, scope, value, cache_duration=None, calculation_time=0):