Just for discuss, not to be resolved in this PR:

Now an attribute's value is not always a String, this class is not valid both for Json an XML anymore. Thus, at least it should be splited into JsonNotifyContextRequest and XMLNotifyContextRequest. The funny thing is that almost all the class "declarations" (in the sense of class name, attributes and methods' semantic) are still valid, and that suggests the idea of having an hierarchy; or an abstract class implemented by JsonNotifyContextRequest and XMLNotifyContextRequest; or an interface in order to define such "declaration". I do not know what is the best approach...