This occurs on slf4j-api 1.5.7 and 1.5.8 when using logback 0.9.18
It does not occur on slf4j-api 1.5.6

Note: the environment being used has various java.endorsed.dirs setup where the logging is initialized. This being not very normal, it could be the reason for this NPE, as I believe LoggerFactory.class.getClassLoader() will return null in this scenario.

java.lang.NullPointerException
at org.slf4j.LoggerFactory.singleImplementationSanityCheck(LoggerFactory.java:192)
at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:113)
at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:269)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:242)
at org.eclipse.jetty.util.log.Slf4jLog.<init>(Slf4jLog.java:33)
at org.eclipse.jetty.util.log.Slf4jLog.<init>(Slf4jLog.java:28)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:355)
at java.lang.Class.newInstance(Class.java:308)