If raven failed to init correctly then you can't close the appender.

Log4j can close the appender when it resets all it's logging configuration from something like a FileWatchdog. Here is the stack trace we got.

@4000000052024a530371f734 Exception in thread "FileWatchdog" java.lang.NullPointerException 
@4000000052024a53037202ec at net.kencochrane.raven.log4j.SentryAppender.close(SentryAppender.java:230) 
@4000000052024a5303720abc at org.apache.log4j.helpers.AppenderAttachableImpl.removeAllAppenders(AppenderAttachableImpl.java:141) 
@4000000052024a530372128c at org.apache.log4j.Category.removeAllAppenders(Category.java:891) 
@4000000052024a5303721674 at org.apache.log4j.PropertyConfigurator.parseCategory(PropertyConfigurator.java:726) 
@4000000052024a530372b69c at org.apache.log4j.PropertyConfigurator.configureRootCategory(PropertyConfigurator.java:615) 
@4000000052024a530372be6c at org.apache.log4j.PropertyConfigurator.doConfigure(PropertyConfigurator.java:502) 
@4000000052024a530372c63c at org.apache.log4j.PropertyConfigurator.doConfigure(PropertyConfigurator.java:395) 
@4000000052024a530372ca24 at org.apache.log4j.PropertyWatchdog.doOnChange(PropertyConfigurator.java:922) 
@4000000052024a530372ddac at org.apache.log4j.helpers.FileWatchdog.checkAndConfigure(FileWatchdog.java:89) 
@4000000052024a530372e57c at org.apache.log4j.helpers.FileWatchdog.run(FileWatchdog.java:108)