presto-main/src/main/java/io/prestosql/cost/ValuesStatsRule.java/ValuesStatsRule/getSymbolValues
class ValuesStatsRule:    private List<Object> getSymbolValues(ValuesNode valuesNode, int symbolId, Session session, Type symbolType)
    {
        if (UNKNOWN.equals(symbolType)) {
            // special casing for UNKNOWN as evaluateConstantExpression does not handle that
            return IntStream.range(0, valuesNode.getRows().size())
                    .mapToObj(rowId -> null)
                    .collect(toList());
        }
        return valuesNode.getRows().stream()
                .map(row -> row.get(symbolId))
                .map(expression -> evaluateConstantExpression(expression, symbolType, metadata, session, ImmutableMap.of()))
                .collect(toList());
    }