NullPointerException in PeriodicSyncFile

[eric]

I haven't been able to see an obvious cause by looking at the code, but here's the backtrace:

java.lang.NullPointerException
    at com.twitter.libkestrel.PeriodicSyncFile$$anonfun$com$twitter$libkestrel$PeriodicSyncFile$$fsync$2.apply$mcVI$sp(PeriodicSyncFile.scala:127)
    at scala.collection.immutable.Range.foreach$mVc$sp(Range.scala:78)
    at com.twitter.libkestrel.PeriodicSyncFile.com$twitter$libkestrel$PeriodicSyncFile$$fsync(PeriodicSyncFile.scala:125)
    at com.twitter.libkestrel.PeriodicSyncFile.flush(PeriodicSyncFile.scala:158)
    at com.twitter.libkestrel.RecordWriter.close(RecordWriter.scala:106)
    at com.twitter.libkestrel.Journal$$anonfun$com$twitter$libkestrel$Journal$$rotate$1.apply$mcV$sp(Journal.scala:307)
    at com.twitter.libkestrel.Journal$$anonfun$com$twitter$libkestrel$Journal$$rotate$1.apply(Journal.scala:291)
    at com.twitter.libkestrel.Journal$$anonfun$com$twitter$libkestrel$Journal$$rotate$1.apply(Journal.scala:291)
    at com.twitter.libkestrel.ReadWriteLock$class.withWriteLock(ReadWriteLock.scala:28)
    at com.twitter.libkestrel.Journal.withWriteLock(Journal.scala:72)
    at com.twitter.libkestrel.Journal.com$twitter$libkestrel$Journal$$rotate(Journal.scala:291)
    at com.twitter.libkestrel.Journal$$anonfun$7.apply(Journal.scala:405)
    at com.twitter.libkestrel.Journal$$anonfun$7.apply(Journal.scala:402)
    at com.twitter.libkestrel.ReadWriteLock$class.withWriteLock(ReadWriteLock.scala:28)
    at com.twitter.libkestrel.Journal.withWriteLock(Journal.scala:72)
    at com.twitter.libkestrel.Journal.put(Journal.scala:402)
    at com.twitter.libkestrel.JournaledQueue.put(JournaledQueue.scala:218)