ERROR [CompactionExecutor:15] 2014-10-31 15:28:32,318 CassandraDaemon.java:153 - Exception in thread Thread[CompactionExecutor:15,1,main]
java.lang.NullPointerException: null
        at org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy.filterColdSSTables(SizeTieredCompactionStrategy.java:181) ~[apache-cassandra-2.1.1.jar:2.1.1]
        at org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy.getNextBackgroundSSTables(SizeTieredCompactionStrategy.java:83) ~[apache-cassandra-2.1.1.jar:2.1.1]
        at org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy.getNextBackgroundTask(SizeTieredCompactionStrategy.java:267) ~[apache-cassandra-2.1.1.jar:2.1.1]
        at org.apache.cassandra.db.compaction.CompactionManager$BackgroundCompactionTask.run(CompactionManager.java:226) ~[apache-cassandra-2.1.1.jar:2.1.1]
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) ~[na:1.7.0_72]
        at java.util.concurrent.FutureTask.run(FutureTask.java:262) ~[na:1.7.0_72]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) ~[na:1.7.0_72]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_72]
        at java.lang.Thread.run(Thread.java:745) [na:1.7.0_72]