code: static String unknownQualityScores(final int length) {
          StringBuilder sb = new StringBuilder(length);
          for (int i = 0; i < length; i++) {
              sb.append("B");
          }
          return sb.toString();
      }
docs: Return unknown quality scores ("B") for a slice with the specified length.
  
  @param length slice length
  @return unknown quality scores ("B") for a slice with the specified length