presto-main/src/main/java/io/prestosql/sql/planner/optimizations/PropertyDerivations.java/Visitor/visitEnforceSingleRow
class Visitor:        @Override
        public ActualProperties visitEnforceSingleRow(EnforceSingleRowNode node, List<ActualProperties> inputProperties)
        {
            return Iterables.getOnlyElement(inputProperties);
        }