Errors logged from firewall migration for new/updated maven-metadata.xml files

Set up Nexus Repo 2.14.9 with firewall enabled on the maven-central proxy repository.   Run an upgrade to Nexus Repo 3.13.0, and  proceed with this until you get to the synchronize phase, where it's looking for updates in Nexus 2.x.  Now request a new (not previously cached) maven-metadata.xml file through Nexus Repo 2: 

http://localhost:8081/nexus/content/repositories/central/org/apache/httpcomponents/httpclient/maven-metadata.xml

Observe that Nexus Repo 3 gets an error logged for this:

2018-08-29 12:45:09,592-0500 ERROR [plan-executor-10-thread-3] admin com.sonatype.nexus.migration.repository.ProcessChangesStep - Failed processing of CREATE central:/org/apache/httpcomponents/httpclient/maven-metadata.xml, will ignore and move on. null
java.lang.NullPointerException: null
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:882)
at com.sonatype.nexus.migration.repository.migrators.Maven2RepositoryMigratorSupport.getIngestedContent(Maven2RepositoryMigratorSupport.java:206)
at com.sonatype.nexus.migration.repository.migrators.RepositoryMigratorSupport.lambda$0(RepositoryMigratorSupport.java:172)
at com.sonatype.nexus.migration.firewall.EnabledFirewallMigrationFacadeImpl.updateAssetAttributes(EnabledFirewallMigrationFacadeImpl.java:225)
at com.sonatype.nexus.migration.firewall.EnabledFirewallMigrationFacadeImpl.lambda$2(EnabledFirewallMigrationFacadeImpl.java:209)
at org.sonatype.nexus.transaction.OperationPoint.lambda$0(OperationPoint.java:53)
at org.sonatype.nexus.transaction.OperationPoint.proceed(OperationPoint.java:64)
at org.sonatype.nexus.transaction.TransactionalWrapper.proceedWithTransaction(TransactionalWrapper.java:56)
at org.sonatype.nexus.transaction.Operations.transactional(Operations.java:200)
at org.sonatype.nexus.transaction.Operations.run(Operations.java:155)
at com.sonatype.nexus.migration.firewall.EnabledFirewallMigrationFacadeImpl.maybeRecordAssetAttributes(EnabledFirewallMigrationFacadeImpl.java:208)
at com.sonatype.nexus.migration.repository.migrators.RepositoryMigratorSupport.createOrUpdate(RepositoryMigratorSupport.java:170)
at com.sonatype.nexus.migration.repository.migrators.RepositoryMigratorSupport.processChange(RepositoryMigratorSupport.java:146)
at com.sonatype.nexus.migration.repository.migrators.Maven2ProxyRepositoryMigrator.processChange(Maven2ProxyRepositoryMigrator.java:118)
at com.sonatype.nexus.migration.repository.RepositoryMigrator$processChange$3.call(Unknown Source)
at com.sonatype.nexus.migration.repository.ProcessChangesStep$_submit_closure2.doCall(ProcessChangesStep.groovy:333)
at com.sonatype.nexus.migration.repository.ProcessChangesStep$_submit_closure2.doCall(ProcessChangesStep.groovy)
at sun.reflect.GeneratedMethodAccessor350.invoke(Unknown Source)

This is because the firewall migration is attempting to find the GAV coordinates of the file:

https://github.com/sonatype/nexus-internal/blob/release-3.13.0-01/private/plugins/nexus-migration-plugin/src/main/java/com/sonatype/nexus/migration/repository/migrators/Maven2RepositoryMigratorSupport.java#L206

The good news is that the affected file is migrated.  And since they are maven-metadata.xml files there isn't anything the firewall migration needed to do with them anyhow.

So this seem to only cause log noise.