public PackageTally combine(PackageTally other) {
        var definedPkgs = Maps.combine(this.definedPackages, other.definedPackages, PackageInfo::hasExportPackageOrElse);
        Set<String> referencedPkgs = new HashSet<>(this.referencedPackagesUnfiltered);
        referencedPkgs.addAll(other.referencedPackagesUnfiltered);

        return new PackageTally(definedPkgs, referencedPkgs);
    }
Represents the classes for two package tallies that are deployed as a single unit.
<p>
ExportPackageAnnotations from this has precedence over the other.
TODO: Add unit test and try using Map.merge (as in the functions below). Can't see how Maps.combine is any different.
bundle-plugin/src/main/java/com/yahoo/container/plugin/classanalysis/PackageTally.java