private int safeHash(Map<Prop, Object> d) {
Set<Entry<Prop, Object>> ee = d.entrySet();
int c = 0;
for (Entry<Prop, Object> e : ee) {
Prop k = e.getKey();
Object v = e.getValue();
c += k.hashCode();
c += (v == null ? 0 : v.hashCode());
}
return c;
}
