In order to fix the Json problem, I put in the OrionRestHandler.java code (line 118) the following sentence:

    data = data.replaceAll("contextValue", "value");

This is done independently of the format of the data (Json or XML), thus, it is always "value".

Nevertheless, since this class is going to be splited into XMLNotifyContextRequest and JsonNotifyContextRequest, this can be fixed in a next PR in a more elegant way.