Nexus 2 to 3 migration fails if there are staging build promotion repositories.

An upgrade from Nexus 2.x to 3.x will fail if Nexus 2.x has staging build promotion repositories.   The repositories migration list will not even load.  The logs show this error:

2018-05-02 14:11:03,506-0600 ERROR [pool-21-thread-3] admin org.sonatype.nexus.extdirect.internal.ExtDirectServlet - Failed to invoke action method: migration_Repository.read, java-method: com.sonatype.nexus.migration.ui.RepositoryComponent.read
java.lang.NullPointerException: Cannot get property 'memberNames' on null object
at org.codehaus.groovy.runtime.NullObject.getProperty(NullObject.java:60)
at org.codehaus.groovy.runtime.InvokerHelper.getProperty(InvokerHelper.java:174)
at org.codehaus.groovy.runtime.DefaultGroovyMethods.getAt(DefaultGroovyMethods.java:257)
at org.codehaus.groovy.runtime.dgm$241.invoke(Unknown Source)
at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoMetaMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:251)
at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.call(PogoMetaMethodSite.java:71)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.NullCallSite.call(NullCallSite.java:35)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:58)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
at com.sonatype.nexus.migration.ui.RepositoryComponent$_closure3.doCall(RepositoryComponent.groovy:144)

Expected

There isn't currently an upgrade path from Nexus 2.x staging to Nexus 3.x staging, so it is expected that the the build promotion repositories should show up in the migration repository list as disabled.