public Builder traceId(String traceId) {
      if (traceId == null) throw new NullPointerException("traceId == null");
      if (traceId.length() == 32) {
        traceIdHigh = lowerHexToUnsignedLong(traceId, 0);
      }
      this.traceId = lowerHexToUnsignedLong(traceId);
      return this;
    }
Same as {@link Span.Builder#traceId(String)}
zipkin/src/main/java/zipkin2/v1/V1Span.java