Converting log items to lucene index entries throws an NPE if a user can't be found

java.lang.NullPointerException
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer.indexLogItem(DefaultReviewItemIndexer.java:420)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer.access$500(DefaultReviewItemIndexer.java:64)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer$IndexOperationIterator.doNext(DefaultReviewItemIndexer.java:171)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer$2.perform(DefaultReviewItemIndexer.java:254)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer$2.perform(DefaultReviewItemIndexer.java:250)
	at com.cenqua.fisheye.lucene.LuceneConnection.withWriter(LuceneConnection.java:525)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer.indexInBatches(DefaultReviewItemIndexer.java:250)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer.access$600(DefaultReviewItemIndexer.java:64)
	at com.atlassian.crucible.activity.lucene.DefaultReviewItemIndexer$3.run(DefaultReviewItemIndexer.java:470)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)