static void zeroAllFieldsOfTypeExcept(O o, Class type, S... exceptions) {
  zeroAllFieldsOfTypeExcept(o, type, asSet(exceptions));
}

static void zeroAllFieldsOfTypeExcept(O o, Class type, Collection<S> exceptions) {
  Set<S> set = asSet(exceptions);
  for (S field : allFields(o))
    if (!set.contains(field) && instanceOf(getOpt(o, field), type))
      set(o, field, null);
}