apollo-client/src/main/java/com/ctrip/framework/apollo/util/OrderedProperties.java/OrderedProperties/entrySet
class OrderedProperties:  @Override
  public Set<Entry<Object, Object>> entrySet() {
    Set<Entry<Object, Object>> original = super.entrySet();
    LinkedHashMap<Object, Entry<Object, Object>> entryMap = new LinkedHashMap<>();
    for (String propertyName : propertyNames) {
      entryMap.put(propertyName, null);
    }

    for (Entry<Object, Object> entry : original) {
      entryMap.put(entry.getKey(), entry);
    }

    return new LinkedHashSet<>(entryMap.values());
  }