@Override
    public String toString() {
        return "PingSession{" +
                "transportId=" + transportId +
                ", sessionId=" + sessionId +
                ", header='" + header + '\'' +
                ", eventIdAllocator=" + eventIdAllocator +
                ", updated=" + updated +
                ", lastPingTimeMillis=" + lastPingTimeMillis +
                '}';
    }
@author Woonduk Kang(emeroad)
@author jaehong.kim
collector/src/main/java/com/navercorp/pinpoint/collector/grpc/lifecycle/PingSession.java