docs: public static String cleanFileName(String badFileName)
      {
          if (badFileName == null)
              return null;
  
          StringBuilder cleanName = new StringBuilder();
          for (int i = 0; i < badFileName.length(); i++)
          {
              int c = (int) badFileName.charAt(i);
              if (Character.isJavaIdentifierPart(c))
                  cleanName.append((char) c);
              else
                  cleanName.append('_');
          }
          return cleanName.toString();
      }