QVT12 — Resolve expressions without source variable

In contrast to 8.2.1.23 ResolveInExp, the prior section 8.2.1.22 ResolveExp does not explicitly state whether the source variable is optional for resolve expressions. For Eclipse QVTo, this leads to the situation the source variable is assumed to be mandatory. Consequently, the resolve expression in following snippet is invalid in Eclipse:

var p : EPackage = resolveone(EPackage);

I don't think that this restriction is desirable from the specification viewpoint.

Eclipse bugzilla: https://bugs.eclipse.org/bugs/show_bug.cgi?id=392156

The resolve needs a domain in which to search for target objects. For ResolveInExp this can be the
traces of a designated mapping. For ResolveExp it would seem that some source objects must be
supplied. However there seems no reason to prohibit a search everywhere and this could be achieved
by specifying Element.allInstances(). Therefore an omitted ResolveExp sources can mean search all
traces.