List<Span> decodeList(BytesDecoder<Span> decoder, byte[] serialized) {
    List<Span> out = new ArrayList<>();
    decoder.decodeList(serialized, out);
    return out;
  }
Before calling this, call {@link CollectorMetrics#incrementMessages()}, and {@link
CollectorMetrics#incrementBytes(int)}. Do not call any other metrics callbacks as those are
handled internal to this method.

@param serializedSpans not empty message
zipkin-collector/core/src/main/java/zipkin2/collector/Collector.java