JSONNull is a singleton class implements Serializable, but don't have "readResolve" method

[eyougo]

JSONNull is a singleton class implements Serializable, but don't have "readResolve" method.
So when serialize JSONNull object in Memcache, and deserializes it, it create a new JSONNull object instance, JSONUtil.isNull() can't judge this correctly.

About "readResolve" method, refer to: http://docs.oracle.com/javase/7/docs/platform/serialization/spec/input.html#5903
About singleton class implements Serializable, refer to:
http://stackoverflow.com/questions/3930181/how-to-deal-with-singleton-along-with-serialization

[aalmiray]

This is not an easy task to fix due to compatibility issues

[eyougo]

Why?
Could you talk about some details, please?