java.lang.NullPointerException

java.lang.NullPointerException
	at hk.ust.tsrs.web.controller.ImageController.handleRequestInternal(ImageController.java:61)
	at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:153)
	at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:44)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:723)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:663)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:394)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:348)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
	at hk.ust.tsrs.web.common.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:135)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
	at hk.ust.celt.cas.client.web.filter.UserNameAdaptorFilter.doFilter(UserNameAdaptorFilter.java:60)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
	at edu.yale.its.tp.cas.client.filter.CASFilter.doFilter(CASFilter.java:317)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:210)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870)
	at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
	at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
	at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
	at java.lang.Thread.run(Thread.java:595)