upgrade to Nexus 3 fails if Nexus 2 has no anonymous user defined

2016-11-01 15:29:43,486+0100 WARN  [plan-executor-5-thread-2] admin com.sonatype.nexus.migration.config.ConfigurationStep - Upgrade configuration: security.anonymous failed
javax.ws.rs.InternalServerErrorException: HTTP 500 Internal Server Error
	at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.handleErrorStatus(ClientInvocation.java:209) [org.sonatype.nexus.siesta:3.1.0.04]
	at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.extractResult(ClientInvocation.java:174) [org.sonatype.nexus.siesta:3.1.0.04]
	at org.jboss.resteasy.client.jaxrs.internal.proxy.extractors.BodyEntityExtractor.extractEntity(BodyEntityExtractor.java:59) [org.sonatype.nexus.siesta:3.1.0.04]
	at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientInvoker.invoke(ClientInvoker.java:104) [org.sonatype.nexus.siesta:3.1.0.04]
	at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientProxy.invoke(ClientProxy.java:64) [org.sonatype.nexus.siesta:3.1.0.04]
	at com.sonatype.nexus.migration.config.$Proxy190.get(Unknown Source) [com.sonatype.nexus.plugins.nexus-migration-plugin:3.1.0.04]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [na:1.8.0_111]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) [na:1.8.0_111]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [na:1.8.0_111]
	at java.lang.reflect.Method.invoke(Method.java:498) [na:1.8.0_111]
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoCachedMethodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:233) [groovy-all:2.4.4]
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56) [groovy-all:2.4.4]
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:133) [groovy-all:2.4.4]
	at com.sonatype.nexus.migration.config.ConfigurationIngesterSupport.get(ConfigurationIngesterSupport.groovy:76) [com.sonatype.nexus.plugins.nexus-migration-plugin:3.1.0.04]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [na:1.8.0_111]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) [na:1.8.0_111]

2016-11-01 15:29:43 WARN [qtp782082420-94] - org.sonatype.sisu.siesta.server.internal.mappers.ThrowableExceptionMapper - org.sonatype.security.usermanagement.UserNotFoundException: User: 'anonymous' could not be found. 
at org.sonatype.security.DefaultSecuritySystem.getUser(DefaultSecuritySystem.java:447) ~[nexus-security-2.14.1-01.jar:2.14.1-01]
at org.sonatype.security.SecuritySystem$getUser.call(Unknown Source) ~[na:na]
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48) ~[na:na]
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113) ~[na:na]
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125) ~[na:na]
at com.sonatype.nexus.migrationagent.config.SecurityAnonymousExtractor.getConfiguration(SecurityAnonymousExtractor.groovy:53) ~[na:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_111]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_111]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_111]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_111]
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93) ~[na:na]
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325) ~[na:na]
at org.codehaus.groovy.runtime.metaclass.MethodMetaProperty$GetBeanMethodMetaProperty.getProperty(MethodMetaProperty.java:76) ~[na:na]
at org.codehaus.groovy.runtime.callsite.GetEffectivePogoPropertySite.getProperty(GetEffectivePogoPropertySite.java:85) ~[na:na]
at org.codehaus.groovy.runtime.callsite.GetEffectivePogoPropertySite.callGetProperty(GetEffectivePogoPropertySite.java:45) ~[na:na]
at com.sonatype.nexus.migrationagent.rest.ConfigurationResource.get(ConfigurationResource.groovy:55) ~[na:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_111]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_111]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_111]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_111]
at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) ~[nexus-siesta-plugin-2.14.1-01/:na]
at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ObjectOutInvoker._dispatch(AbstractResourceMetho