Defer the failure until instantiation.

When it is used in the signature, I'm getting the following exception:

SEVERE: Failed to create Guice container from all the plugins
com.google.inject.internal.guava.collect.$ComputationException: java.lang.NoClassDefFoundError: org/jenkinsci/plugins/multiplescms/MultiSCM
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:397)
	at com.google.inject.internal.FailableCache.get(FailableCache.java:49)
	at com.google.inject.internal.MembersInjectorStore.get(MembersInjectorStore.java:66)
	at com.google.inject.internal.ConstructorInjectorStore.createConstructor(ConstructorInjectorStore.java:74)
	at com.google.inject.internal.ConstructorInjectorStore.access$000(ConstructorInjectorStore.java:29)
	at com.google.inject.internal.ConstructorInjectorStore$1.create(ConstructorInjectorStore.java:37)
	at com.google.inject.internal.ConstructorInjectorStore$1.create(ConstructorInjectorStore.java:33)
	at com.google.inject.internal.FailableCache$1.apply(FailableCache.java:38)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingValueReference.compute(ComputingConcurrentHashMap.java:355)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingSegment.compute(ComputingConcurrentHashMap.java:184)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingSegment.getOrCompute(ComputingConcurrentHashMap.java:153)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap.getOrCompute(ComputingConcurrentHashMap.java:69)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:393)
	at com.google.inject.internal.FailableCache.get(FailableCache.java:49)
	at com.google.inject.internal.ConstructorInjectorStore.get(ConstructorInjectorStore.java:50)
	at com.google.inject.internal.ConstructorBindingImpl.initialize(ConstructorBindingImpl.java:137)
	at com.google.inject.internal.InjectorImpl.initializeBinding(InjectorImpl.java:537)
	at com.google.inject.internal.AbstractBindingProcessor$Processor$1.run(AbstractBindingProcessor.java:160)
	at com.google.inject.internal.ProcessedBindingData.initializeBindings(ProcessedBindingData.java:44)
	at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:123)
	at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:107)
	at com.google.inject.Guice.createInjector(Guice.java:96)
	at com.google.inject.Guice.createInjector(Guice.java:73)
	at hudson.ExtensionFinder$GuiceFinder.<init>(ExtensionFinder.java:282)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
	at java.lang.Class.newInstance0(Class.java:374)
	at java.lang.Class.newInstance(Class.java:327)
	at net.java.sezpoz.IndexItem.instance(IndexItem.java:181)
	at hudson.ExtensionFinder$Sezpoz._find(ExtensionFinder.java:642)
	at hudson.ExtensionFinder$Sezpoz.find(ExtensionFinder.java:617)
	at hudson.ExtensionFinder._find(ExtensionFinder.java:151)
	at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:316)
	at hudson.ExtensionList.load(ExtensionList.java:295)
	at hudson.ExtensionList.ensureLoaded(ExtensionList.java:248)
	at hudson.ExtensionList.iterator(ExtensionList.java:138)
	at hudson.ClassicPluginStrategy.findComponents(ClassicPluginStrategy.java:309)
	at hudson.ExtensionList.load(ExtensionList.java:295)
	at hudson.ExtensionList.ensureLoaded(ExtensionList.java:248)
	at hudson.ExtensionList.size(ExtensionList.java:157)
	at java.util.AbstractCollection.isEmpty(AbstractCollection.java:86)
	at com.cloudbees.jenkins.plugins.license.PluginImpl.postInitialize(PluginImpl.java:31)
	at hudson.PluginManager$2$1$2.run(PluginManager.java:374)
	at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
	at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
	at jenkins.model.Jenkins$7.runTask(Jenkins.java:899)
	at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
	at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
	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:722)
Caused by: java.lang.NoClassDefFoundError: org/jenkinsci/plugins/multiplescms/MultiSCM
	at java.lang.Class.getDeclaredMethods0(Native Method)
	at java.lang.Class.privateGetDeclaredMethods(Class.java:2451)
	at java.lang.Class.getDeclaredMethods(Class.java:1810)
	at com.google.inject.spi.InjectionPoint.getInjectionPoints(InjectionPoint.java:674)
	at com.google.inject.spi.InjectionPoint.forInstanceMethodsAndFields(InjectionPoint.java:366)
	at com.google.inject.internal.MembersInjectorStore.createWithListeners(MembersInjectorStore.java:91)
	at com.google.inject.internal.MembersInjectorStore.access$000(MembersInjectorStore.java:35)
	at com.google.inject.internal.MembersInjectorStore$1.create(MembersInjectorStore.java:43)
	at com.google.inject.internal.MembersInjectorStore$1.create(MembersInjectorStore.java:40)
	at com.google.inject.internal.FailableCache$1.apply(FailableCache.java:38)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingValueReference.compute(ComputingConcurrentHashMap.java:355)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingSegment.compute(ComputingConcurrentHashMap.java:184)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingSegment.getOrCompute(ComputingConcurrentHashMap.java:153)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap.getOrCompute(ComputingConcurrentHashMap.java:69)
	at com.google.inject.internal.guava.collect.$ComputingConcurrentHashMap$ComputingMapAdapter.get(ComputingConcurrentHashMap.java:393)
	... 52 more
Caused by: java.lang.ClassNotFoundException: org.jenkinsci.plugins.multiplescms.MultiSCM
	at org.apache.tools.ant.AntClassLoader.findClassInComponents(AntClassLoader.java:1365)
	at org.apache.tools.ant.AntClassLoader.findClass(AntClassLoader.java:1315)
	at org.apache.tools.ant.AntClassLoader.loadClass(AntClassLoader.java:1068)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
	... 67 more

src/main/java/com/cloudbees/jenkins/GitHubRepositoryNameContributor.java

@@ -90,7 +90,7 @@ public void parseAssociatedNames(AbstractProject<?, ?> job, Collection<GitHubRep
     @Extension(optional=true)
     public static class FromMultiSCM extends AbstractFromSCMImpl {
         // make this class fail to load if MultiSCM is not present
-        private MultiSCM signature() { return null; }
+        public FromMultiSCM() { MultiSCM.class.toString(); }
 
         @Override
         public void parseAssociatedNames(AbstractProject<?, ?> job, Collection<GitHubRepositoryName> result) {