If you run a blob restore the npm metadata (package root) repair will be run and you will see the following in the logs
2018-11-05 15:28:11,690-0400 INFO [quartz-2-thread-5] *SYSTEM org.sonatype.nexus.repository.npm.repair.NpmRepairPackageRootComponent - Beginning processing all npm packages for repair
This is true even if an npm repository does not exist. It also ignores the blob store setting in the blob restore task i.e. all npm repositories will have their metadata generated even if you were just running a blob restore for a blobstore that was used by a single docker (or any other format) repository
- Npm package root repair is only run for npm repositories that have had components or assets restored.