Nullpointer during Jenkins startup caused by Email Extension Plugin

java.io.IOException: Unable to read /opt/jenkins/hudson.plugins.emailext.ExtendedEmailPublisher.xml
at hudson.XmlFile.unmarshal(XmlFile.java:165)
at hudson.model.Descriptor.load(Descriptor.java:783)
at hudson.plugins.emailext.ExtendedEmailPublisherDescriptor.<init>(ExtendedEmailPublisherDescriptor.java:344)
at hudson.plugins.emailext.ExtendedEmailPublisherDescriptor$$FastClassByGuice$$5dfa54d0.newInstance(<generated>)
at com.google.inject.internal.cglib.reflect.$FastConstructor.newInstance(FastConstructor.java:40)
at com.google.inject.internal.DefaultConstructionProxyFactory$1.newInstance(DefaultConstructionProxyFactory.java:61)
at com.google.inject.internal.ConstructorInjector.provision(ConstructorInjector.java:108)
at com.google.inject.internal.ConstructorInjector.construct(ConstructorInjector.java:88)
at com.google.inject.internal.ConstructorBindingImpl$Factory.get(ConstructorBindingImpl.java:269)
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:428)
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:390)
at hudson.ExtensionFinder$GuiceFinder.find(ExtensionFinder.java:381)
at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:386)
at hudson.ExtensionList.load(ExtensionList.java:349)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:287)
at hudson.ExtensionList.iterator(ExtensionList.java:156)
at jenkins.model.Jenkins.getDescriptorByType(Jenkins.java:1197)
at hudson.plugins.copyartifact.BuildSelectorParameter.initAliases(BuildSelectorParameter.java:135)
at hudson.plugins.copyartifact.CopyArtifactPlugin.postInitialize(CopyArtifactPlugin.java:35)
at hudson.PluginManager$2$1$2.run(PluginManager.java:390)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:282)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:905)
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:1157)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:627)
at java.lang.Thread.run(Thread.java:801)
Caused by: com.thoughtworks.xstream.converters.ConversionException: Could not call hudson.plugins.emailext.ExtendedEmailPublisherDescriptor.readResolve() : null : Could not call hudson.plugins.emailext.ExtendedEmailPublisherDescriptor.readResolve() : null