Malformed JSON Response on Exception

It seems the JSON generated for the response due to an Exception in controller's aspects is malformed.
The closeTry() method in WebJsonMetadata.java append the current line :

{\\\"ERROR\\\":\"+e.getMessage()+\"\\\"}

This generate this sort of response :

{"ERROR":MY_EXCEPTION_MESSAGE"}

The line should be

{\\\"ERROR\\\":\\\"\"+e.getMessage()+\"\\\"}