public static Set<String> convertSubregionsStringToSet(String subregionsString) {
		return isEmpty(subregionsString) ? emptySet() : new HashSet<>(asList(subregionsString.split(",")));
	}
Convert configured string type of subregion value to {@link Set}.

@param subregionsString value of 'ngrinder.cluster.subregion' in system-ex.conf, it concatenates with ',' like sub1,sub2
ngrinder-controller/src/main/java/org/ngrinder/common/util/RegionUtils.java