docs: private boolean folderContainsFiles(File folder) {
          if (folder != null) {
              File[] files = folder.listFiles();
              for (File file : files)
                  if (file.isFile())
                      return true;
              for (File file : files)
                  if (file.isDirectory())
                      if (folderContainsFiles(file))
                          return true;
          }
          return false;
      }