i have written one Custom Tag lib in jsf , and getting following error

[Pushpa devi]

java.lang.NullPointerException
at javax.faces.component.UIComponentBase.findComponent(UIComponentBase.java:478)
at coreservlets.GreaterThanValidator.validate(GreaterThanValidator.java:21)
at javax.faces.component.UIInput.validateValue(UIInput.java:770)
at javax.faces.component.UIInput.validate(UIInput.java:634)
at javax.faces.component.UIInput.executeValidate(UIInput.java:838)
at javax.faces.component.UIInput.processValidators(UIInput.java:412)
at javax.faces.component.UIForm.processValidators(UIForm.java:170)
at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:904)
at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:342)
at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:78)
at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:200)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:90)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:197)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)