code: public static String deriveFault(Span span) {
          List<SpanHttpDeriverUtil.HttpCode> errorCodes =
                  SpanHttpDeriverUtil.getClientOrServerErrors(SpanHttpDeriverUtil.getHttpStatusCodes(span.getBinaryAnnotations()));
  
          if (errorCodes.size() > 0) {
              return errorCodes.iterator().next().getDescription();
          }
  
          return null;
      }
docs: Derives fault from Span. Fault is determined by HTTP client/server error code contained in binary annotations.
  
  @param span the span
  @return fault ()