code: public void validateFileDoesNotExist(UIInput<String> directory, UIInput<String> fileName, UIValidationContext validator) {
          String resourcePath = CamelXmlHelper.createFileName(directory, fileName);
          if (files.contains(resourcePath)) {
              validator.addValidationError(fileName, "A file with that name already exists!");
          }
      }
docs: Validates that the given selected directory and fileName are valid and that the file doesn't already exist