public OsVersionChange withTarget(Version version, NodeType nodeType) {
        var copy = new TreeMap<>(this.targets);
        copy.compute(nodeType, (key, prevTarget) -> new OsVersionTarget(nodeType, version));
        return new OsVersionChange(copy);
    }
Returns a copy of this with given target added
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/os/OsVersionChange.java