Generated XML does not distinguish "new HashSet()" from "new HashSet<>()"

[michaelhkay]

The XML serializer does not distinguish an empty NodeList property from a null NodeList property.

In consequence "new HashSet()" and "new HashSet<>()" produce the same output: in one case type.typeArguments is null, in the other case it is empty.

[michaelhkay]

I've changed XmlPrinter so it now outputs an empty NodeList property as an empty element: with new HashSet<>(40) we now get

                     <initializer nodeType="ObjectCreationExpr">
                        <type nodeType="ClassOrInterfaceType">
                           <name nodeType="SimpleName" identifier="HashSet"/>
                           <typeArguments/>
                           <annotations/>
                        </type>
                        <arguments>
                           <argument nodeType="IntegerLiteralExpr" value="40"/>
                        </arguments>
                     </initializer>

(Note the empty <typeArguments/> element). This gives me the information needed to distinguish these two cases. I realise that doing this for all empty NodeLists could (a) inflate the XML size, and (b) cause backwards compatibility issues for existing users, but it works for me.

[michaelhkay]

Making this change for all properties of all nodes does turn out to be rather disruptive. So perhaps the change needs to be confined to cases where there is actually a semantic difference between a null property and an empty property? Unfortunately it's not easy to enumerate those cases.