code: @Override
      public String decodeExtractedValue(String tokenName, String value) {
          if (value == null || value.equals("")) {
              return value;
          }
  
          // In Apache logfiles a '-' means a 'not specified' / 'empty' value.
          if (value.equals("-")) {
              return null;
          }
  
          return value;
      }
docs: --------------------------------------------