If you disable maven plugin, and open configuration of a project you will see jetty exception. It does not matter if project uses or not maven. Mine did not, but configuration page still tried to load maven, which was disabled as i don't use it.

WARNING: Failed to load hudson.maven.MavenModuleSet
java.lang.InstantiationException: java.lang.NoClassDefFoundError: Could not initialize class hudson.maven.MavenModuleSet$DescriptorImpl
at net.java.sezpoz.IndexItem.instance(IndexItem.java:193)
at hudson.ExtensionFinder$GuiceFinder.instantiate(ExtensionFinder.java:355)
at hudson.ExtensionFinder$GuiceFinder.access$700(ExtensionFinder.java:234)
at hudson.ExtensionFinder$GuiceFinder$SezpozModule$1.get(ExtensionFinder.java:531)
at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:86)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.provision(InternalFactoryToInitializableAdapter.java:55)
at com.google.inject.internal.ProviderInternalFactory.circularGet(ProviderInternalFactory.java:66)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.get(InternalFactoryToInitializableAdapter.java:47)
at com.google.inject.internal.ProviderToInternalFactoryAdapter$1.call(ProviderToInternalFactoryAdapter.java:46)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1058)
at com.google.inject.internal.ProviderToInternalFactoryAdapter.get(ProviderToInternalFactoryAdapter.java:40)
at com.google.inject.Scopes$1$1.get(Scopes.java:65)
at hudson.ExtensionFinder$GuiceFinder$FaultTolerantScope$1.get(ExtensionFinder.java:429)
at com.google.inject.internal.InternalFactoryToProviderAdapter.get(InternalFactoryToProviderAdapter.java:41)
at com.google.inject.internal.InjectorImpl$3$1.call(InjectorImpl.java:1005)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1051)
at com.google.inject.internal.InjectorImpl$3.get(InjectorImpl.java:1001)
at hudson.ExtensionFinder$GuiceFinder._find(ExtensionFinder.java:391)
at hudson.ExtensionFinder$GuiceFinder.find(ExtensionFinder.java:382)
at hudson.ExtensionFinder._find(ExtensionFinder.java:151)
at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:317)
at hudson.ExtensionList.load(ExtensionList.java:295)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:248)
at hudson.ExtensionList.getComponents(ExtensionList.java:149)
at hudson.DescriptorExtensionList.load(DescriptorExtensionList.java:182)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:248)
at hudson.ExtensionList.iterator(ExtensionList.java:138)
at org.jenkinsci.plugins.xunit.AliasInitializer.addAliases(AliasInitializer.java:23)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at hudson.init.TaskMethodFinder.invoke(TaskMethodFinder.java:105)
at hudson.init.TaskMethodFinder$TaskImpl.run(TaskMethodFinder.java:169)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:904)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:210)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:679)
Caused by: java.lang.NoClassDefFoundError: Could not initialize class hudson.maven.MavenModuleSet$DescriptorImpl
at hudson.maven.MavenModuleSet.<clinit>(MavenModuleSet.java:1217)
at sun.misc.Unsafe.ensureClassInitialized(Native Method)
at sun.reflect.UnsafeFieldAccessorFactory.newFieldAccessor(UnsafeFieldAccessorFactory.java:43)
at sun.reflect.ReflectionFactory.newFieldAccessor(ReflectionFactory.java:140)
at java.lang.reflect.Field.acquireFieldAccessor(Field.java:936)
at java.lang.reflect.Field.getFieldAccessor(Field.java:917)
at java.lang.reflect.Field.get(Field.java:376)
at net.java.sezpoz.IndexItem.instance(IndexItem.java:185)
... 40 more