Differential and Difference Equations

Error number 4001 in 4: Error while parsing velocity page Subjects.Differential_and_Difference_Equations
Wrapped Exception: Failed to evaluate content with id Differential_and_Difference_Equations
com.xpn.xwiki.XWikiException: Error number 4001 in 4: Error while parsing velocity page Subjects.Differential_and_Difference_Equations
Wrapped Exception: Failed to evaluate content with id Differential_and_Difference_Equations
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:112)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.render(XWikiVelocityRenderer.java:87)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:273)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:203)
	at com.xpn.xwiki.XWiki.include(XWiki.java:3621)
	at com.xpn.xwiki.api.XWiki.includeForm(XWiki.java:1372)
	at com.xpn.xwiki.api.XWiki.includeForm(XWiki.java:1338)
	at sun.reflect.GeneratedMethodAccessor127.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:294)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:194)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:170)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.render(XWikiVelocityRenderer.java:87)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:273)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:203)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:171)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderDocument(DefaultXWikiRenderingEngine.java:160)
	at com.xpn.xwiki.doc.XWikiDocument.getRenderedContent(XWikiDocument.java:430)
	at com.xpn.xwiki.api.Document.getRenderedContent(Document.java:371)
	at sun.reflect.GeneratedMethodAccessor165.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:294)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:107)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:107)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1648)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1575)
	at com.xpn.xwiki.api.XWiki.parseTemplate(XWiki.java:608)
	at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:294)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:194)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:170)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:88)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:88)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1648)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1575)
	at com.xpn.xwiki.web.Utils.parseTemplate(Utils.java:125)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:226)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:115)
	at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
	at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
	at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
	at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:112)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:185)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:151)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:269)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:300)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:680)

Wrapped Exception:

org.apache.velocity.exception.MethodInvocationException: Invocation of method 'expandSubjectQuery' in  class net.i2geo.xwiki.impl.DefaultSearchI2GXWiki threw exception java.lang.NullPointerException @ Subjects.Differential_and_Difference_Equations22,30?
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:286)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.value(ASTReference.java:419)
	at org.apache.velocity.runtime.parser.node.ASTExpression.value(ASTExpression.java:73)
	at org.apache.velocity.runtime.parser.node.ASTSetDirective.render(ASTSetDirective.java:125)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:107)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.render(XWikiVelocityRenderer.java:87)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:273)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:203)
	at com.xpn.xwiki.XWiki.include(XWiki.java:3621)
	at com.xpn.xwiki.api.XWiki.includeForm(XWiki.java:1372)
	at com.xpn.xwiki.api.XWiki.includeForm(XWiki.java:1338)
	at sun.reflect.GeneratedMethodAccessor127.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:294)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:194)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:170)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.render(XWikiVelocityRenderer.java:87)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:273)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:203)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderText(DefaultXWikiRenderingEngine.java:171)
	at com.xpn.xwiki.render.DefaultXWikiRenderingEngine.renderDocument(DefaultXWikiRenderingEngine.java:160)
	at com.xpn.xwiki.doc.XWikiDocument.getRenderedContent(XWikiDocument.java:430)
	at com.xpn.xwiki.api.Document.getRenderedContent(Document.java:371)
	at sun.reflect.GeneratedMethodAccessor165.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:294)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:107)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:107)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1648)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1575)
	at com.xpn.xwiki.api.XWiki.parseTemplate(XWiki.java:608)
	at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:203)
	at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:294)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.apache.velocity.runtime.directive.VelocimacroProxy.render(VelocimacroProxy.java:194)
	at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:170)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:88)
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:74)
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:88)
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:318)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:178)
	at org.xwiki.velocity.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:143)
	at com.xpn.xwiki.render.XWikiVelocityRenderer.evaluate(XWikiVelocityRenderer.java:107)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1648)
	at com.xpn.xwiki.XWiki.parseTemplate(XWiki.java:1575)
	at com.xpn.xwiki.web.Utils.parseTemplate(Utils.java:125)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:226)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:115)
	at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
	at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
	at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
	at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:112)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:185)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:151)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:269)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:300)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:680)
Caused by: java.lang.NullPointerException
	at net.i2geo.xwiki.impl.DefaultSearchI2GXWiki.expandSubjectQuery(DefaultSearchI2GXWiki.java:137)
	at sun.reflect.GeneratedMethodAccessor402.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:295)
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:245)
	… 106 more