presto-accumulo/src/main/java/io/prestosql/plugin/accumulo/index/Indexer.java/Indexer/MetricsKey
class Indexer:        public MetricsKey(ByteBuffer row, ByteBuffer family, ColumnVisibility visibility)
        {
            requireNonNull(row, "row is null");
            requireNonNull(family, "family is null");
            requireNonNull(visibility, "visibility is null");
            this.row = row;
            this.family = family;
            this.visibility = visibility.getExpression() != null ? visibility : EMPTY_VISIBILITY;
        }