When use tomcat 7 apr and servlet 3 gravity servlet,tomcat throw

java.lang.NullPointerException
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilterEvent(ApplicationFilterChain.java:479)
at org.apache.catalina.core.ApplicationFilterChain.doFilterEvent(ApplicationFilterChain.java:372)
at org.apache.catalina.core.StandardWrapperValve.event(StandardWrapperValve.java:434)
at org.apache.catalina.core.StandardContextValve.event(StandardContextValve.java:282)
at org.apache.catalina.valves.ValveBase.event(ValveBase.java:217)
at org.apache.catalina.core.StandardHostValve.event(StandardHostValve.java:221)
at org.apache.catalina.valves.ValveBase.event(ValveBase.java:217)
at org.apache.catalina.valves.ValveBase.event(ValveBase.java:217)
at org.apache.catalina.core.StandardEngineValve.event(StandardEngineValve.java:138)
at org.apache.catalina.connector.CoyoteAdapter.event(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11AprProcessor.event(Http11AprProcessor.java:159)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.event(Http11AprProtocol.java:530)
at org.apache.tomcat.util.net.AprEndpoint$SocketEventProcessor.run(AprEndpoint.java:1587)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)

If change to nio,it's fine.

I don't know is it tomcat 7 bug.