FSWALEntry unloadAppend() {
    FSWALEntry entry = this.entry;
    this.entry = null;
    this.type = Type.EMPTY;
    return entry;
  }
Unload the truck of its {@link FSWALEntry} payload. The internal reference is released.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/RingBufferTruck.java