NPE in OracleClient of Worker

``` java
13:40:57.465 [PathChildrenCache-1] ERROR o.a.c.f.r.cache.PathChildrenCache -
java.lang.NullPointerException: null
at io.fluo.core.oracle.OracleClient$TimestampRetriever.childEvent(OracleClient.java:118) ~[fluo-core-1.0.0-beta-1-SNAPSHOT.jar:1.0.0-beta-1-SNAPSHOT]
at org.apache.curator.framework.recipes.cache.PathChildrenCache$5.apply(PathChildrenCache.java:509) [curator-recipes-2.6.0.jar:na]
at org.apache.curator.framework.recipes.cache.PathChildrenCache$5.apply(PathChildrenCache.java:503) [curator-recipes-2.6.0.jar:na]
at org.apache.curator.framework.listen.ListenerContainer$1.run(ListenerContainer.java:92) [curator-framework-2.6.0.jar:na]
at com.google.common.util.concurrent.MoreExecutors$SameThreadExecutorService.execute(MoreExecutors.java:262) [guava-13.0.1.jar:na]
at org.apache.curator.framework.listen.ListenerContainer.forEach(ListenerContainer.java:83) [curator-framework-2.6.0.jar:na]
at org.apache.curator.framework.recipes.cache.PathChildrenCache.callListeners(PathChildrenCache.java:500) [curator-recipes-2.6.0.jar:na]
at org.apache.curator.framework.recipes.cache.EventOperation.invoke(EventOperation.java:35) [curator-recipes-2.6.0.jar:na]
at org.apache.curator.framework.recipes.cache.PathChildrenCache$10.run(PathChildrenCache.java:762) [curator-recipes-2.6.0.jar:na]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [na:1.7.0_55]
at java.util.concurrent.FutureTask.run(FutureTask.java:262) [na:1.7.0_55]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) [na:1.7.0_55]
at java.util.concurrent.FutureTask.run(FutureTask.java:262) [na:1.7.0_55]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_55]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_55]
at java.lang.Thread.run(Thread.java:745) [na:1.7.0_55]
13:40:57.474 [Thread-10] DEBUG io.fluo.core.oracle.OracleClient - Connecting to oracle at rd6ul-92515i.infosec.tycho.ncsc.mil:9913
13:40:57.484 [Thread-10] INFO io.fluo.core.oracle.OracleClient - Connected to oracle at rd6ul-92515i.infosec.tycho.ncsc.mil:9913
```