If I try to "slice" parameters for my projects I get a empty page. After taking a look into the log files I see the following stack trace:

INFO: Loaded: class configurationslicing.tools.GroovySlicer
Dec 09, 2014 9:08:27 AM hudson.ExpressionFactory2$JexlExpression evaluate
WARNING: Caught exception evaluating: it.configuredValues in /jenkins/slicing/parameters/. Reason: java.lang.reflect.InvocationTargetException
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.commons.jexl.util.PropertyExecutor.execute(PropertyExecutor.java:125)
at org.apache.commons.jexl.util.introspection.UberspectImpl$VelGetterImpl.invoke(UberspectImpl.java:314)
at org.apache.commons.jexl.parser.ASTArrayAccess.evaluateExpr(ASTArrayAccess.java:185)
at org.apache.commons.jexl.parser.ASTIdentifier.execute(ASTIdentifier.java:75)
at org.apache.commons.jexl.parser.ASTReference.execute(ASTReference.java:83)
at org.apache.commons.jexl.parser.ASTReference.value(ASTReference.java:57)
at org.apache.commons.jexl.parser.ASTReferenceExpression.value(ASTReferenceExpression.java:51)
at org.apache.commons.jexl.ExpressionImpl.evaluate(ExpressionImpl.java:80)
at hudson.ExpressionFactory2$JexlExpression.evaluate(ExpressionFactory2.java:74)
at org.apache.commons.jelly.expression.ExpressionSupport.evaluateRecurse(ExpressionSupport.java:61)
at org.apache.commons.jelly.expression.ExpressionSupport.evaluateAsIterator(ExpressionSupport.java:94)
at org.apache.commons.jelly.tags.core.ForEachTag.doTag(ForEachTag.java:89)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.JellyViewScript.run(JellyViewScript.java:95)
at org.kohsuke.stapler.jelly.IncludeTag.doTag(IncludeTag.java:147)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:99)
at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:120)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:99)
at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:120)
at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:99)
at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$1.run(CoreTagLibrary.java:98)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:120)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:99)
at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:120)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.JellyViewScript.run(JellyViewScript.java:95)
at org.kohsuke.stapler.jelly.DefaultScriptInvoker.invokeScript(DefaultScriptInvoker.java:63)
at org.kohsuke.stapler.jelly.DefaultScriptInvoker.invokeScript(DefaultScriptInvoker.java:53)
at org.kohsuke.stapler.jelly.JellyClassTearOff.serveIndexJelly(JellyClassTearOff.java:112)
at org.kohsuke.stapler.jelly.JellyFacet.handleIndexRequest(JellyFacet.java:127)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:735)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$12.dispatch(MetaClass.java:391)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$12.dispatch(MetaClass.java:391)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)
at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:96)
at com.cloudbees.jenkins.support.slowrequest.SlowRequestFilter.doFilter(SlowRequestFilter.java:37)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:99)
at net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:198)
at net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:176)
at net.bull.javamelody.PluginMonitoringFilter.doFilter(PluginMonitoringFilter.java:85)
at org.jvnet.hudson.plugins.monitoring.HudsonMonitoringFilter.doFilter(HudsonMonitoringFilter.java:99)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:99)
at jenkins.metrics.impl.MetricsFilter.doFilter(MetricsFilter.java:117)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:99)
at hudson.plugins.greenballs.GreenBallFilter.doFilter(GreenBallFilter.java:58)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:99)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:88)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.jenkinsci.plugins.reverse_proxy_auth.ReverseProxySecurityRealm$1.doFilter(ReverseProxySecurityRealm.java:454)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:46)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:581)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.ajp.AjpAprProcessor.process(AjpAprProcessor.java:197)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1852)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException