presto-main/src/main/java/io/prestosql/operator/scalar/MathFunctions.java/MathFunctions/mapL2Norm
class MathFunctions:    private static Double mapL2Norm(Block map)
    {
        double norm = 0.0;

        for (int i = 1; i < map.getPositionCount(); i += 2) {
            if (map.isNull(i)) {
                return null;
            }
            norm += DOUBLE.getDouble(map, i) * DOUBLE.getDouble(map, i);
        }

        return Math.sqrt(norm);
    }