@Nullable
    private String collectionStatusMessage() {
      String message = "";
      if (libraries == null) {
        message += "No AdditionalLibraries data provided. ";
      }
      if (contributors == null) {
        message += "No IndexableSetContributor data provided. ";
      }
      if (excludePolicyDescriptors == null) {
        message += "No ExcludeDirectoryPolicy data provided. ";
      }
      return message.isEmpty() ? null : message;
    }
@Nullable
    private String collectionStatusMessage()