The new ant target update_solr_indexes makes use of dspace-api/src/main/java/org/dspace/app/util/IndexVersion.java. IndexVersion.java will attempt to update an empty index, and will fail. In development environments, is possible to have an empty index. This situation is a hinderance to developement, as it requires one to first manually delete the empty index. It also fosters the habit of deleting indexes to resolve issues, which is not a habit we should be encouraging. At this point: https://github.com/DSpace/DSpace/blob/58f7734400ac0b8e2dfc465d92b1b3d5f41c96a9/dspace-api/src/main/java/org/dspace/app/util/IndexVersion.java#L106
The index directory is validated for existence, it would be a simple thing to add one additional validation task to ensure the index is populated. An empty index is, I think, an empty directory, so we could just check to see if the directory is empty and if it is empty, stop any further attempts to identify the index version.