docs: public static String getRelativePath(File file, File folder) {
  
          String filePath = file.getAbsolutePath();
          String folderPath = folder.getAbsolutePath();
  
          if (filePath.startsWith(folderPath)) {
              return filePath.substring(folderPath.length() + 1);
          } else {
              return null;
          }
      }