Still getting this problem, and I didn’t find any useful information while googling. All I learned is that the “namespace” here is an object but in this case it’s null. null return values are said to be legal (http://code.google.com/appengine/docs/java/javadoc/com/google/appengine/api/memcache/MemcacheService.html).
This may be a serialization issue. But I’m just guessing, the reason is that I saw a lot of issues while googling related to serialization of objects in GAE.
If there’s somebody who have tried using Vaadin + GAE, please tell me how you set it up with Eclipse and Vaadin plugin. You might have encountered some specific config that is not mentioned in the Vaadin + GAE Development setup tutorial that could help me. Thank you. 