code: private String getCustSerializedEnumValue(EnumValueOptions options, String defaultValue) {
      for (Extension<EnumValueOptions, String> extension : serializedEnumValueExtensions) {
        if (options.hasExtension(extension)) {
          return options.getExtension(extension);
        }
      }
      return defaultValue;
    }
docs: Retrieves the custom enum value name from the given options, and if not found, returns the
  specified default value.