@Override
protected Map<Server, Integer> read(Preferences pref) throws BackingStoreException {
Map<Server, Integer> result = newMutableData();
for (String name : pref.keys()) {
Server server;
try {
server = Server.valueOf(name);
} catch (IllegalArgumentException e) {
LOG.log(Level.SEVERE, "Skipping unknown server {0}", name);
continue;