Log message for blob store metrics doesn't expand file name

1. Start up Nexus Repo 3.15.2
2. Populate a repository with some content
3. Restart

Observe the following is logged at startup:

2019-01-29 12:47:17,205-0600 INFO  [FelixStartLevel]  *SYSTEM org.sonatype.nexus.blobstore.file.internal.FileBlobStoreMetricsStore - Loading blob store metrics file {}
2019-01-29 12:48:26,537-0600 INFO  [FelixStartLevel]  *SYSTEM org.sonatype.nexus.blobstore.file.internal.FileBlobStoreMetricsStore - Loading blob store metrics file {}

Note that the variable is not expanded properly, so you can't see what blob store metrics file is being loaded.