public static Optional<String> getNamespaceGroup(NamespaceDescriptor namespaceDesc) {
    return Optional
      .ofNullable(namespaceDesc.getConfigurationValue(RSGroupInfo.NAMESPACE_DESC_PROP_GROUP));
  }
Do not allow creating new tables/namespaces which has an empty rs group, expect the default rs
group. Notice that we do not check for online servers, as this is not stable because region
servers can die at any time.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/MasterProcedureUtil.java