While not ideal, you can create a new AttributeTransform that sets a place holder when storing into DynamoDB and removes it when pulling out of DynamoDB as part of your DynamoDBMapper instantiation.
I did this to convert some String Sets (SS) in my database to String Lists (L). I almost did this same thing to fix the empty String issue but didn't have the time to implement it yet.
I did this to convert some String Sets (SS) in my database to String Lists (L). I almost did this same thing to fix the empty String issue but didn't have the time to implement it yet.
http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/ama...