VelocityViewServlet : Error processing a template for path '/servlet/topic'

java.lang.NumberFormatException: null
	at java.lang.Integer.parseInt(Integer.java:415)
	at java.lang.Integer.parseInt(Integer.java:497)
	at com.gss.cms.view.ContentAccessor.findTopicById(ContentAccessor.java:426)
	at sun.reflect.GeneratedMethodAccessor103.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:585)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:267)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:197)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:175)
	at org.apache.velocity.runtime.parser.node.ASTReference.value(ASTReference.java:327)
	at org.apache.velocity.runtime.parser.node.ASTExpression.value(ASTExpression.java:51)
	at org.apache.velocity.runtime.parser.node.ASTSetDirective.render(ASTSetDirective.java:95)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:230)
	at org.apache.velocity.Template.merge(Template.java:256)
	at org.apache.velocity.tools.view.servlet.VelocityLayoutServlet.mergeTemplate(VelocityLayoutServlet.java:224)
	at org.apache.velocity.tools.view.servlet.VelocityViewServlet.doRequest(VelocityViewServlet.java:551)
	at org.apache.velocity.tools.view.servlet.VelocityViewServlet.doGet(VelocityViewServlet.java:507)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
	at com.gss.fln.FLNDispatchServlet.service(FLNDispatchServlet.java:342)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	at java.lang.Thread.run(Thread.java:595)