presto-main/src/main/java/io/prestosql/operator/scalar/MapSubscriptOperator.java/MapSubscriptOperator/subscript
class MapSubscriptOperator:    @UsedByGeneratedCode
    public static Object subscript(MissingKeyExceptionFactory missingKeyExceptionFactory, Type keyType, Type valueType, ConnectorSession session, Block map, Object key)
    {
        SingleMapBlock mapBlock = (SingleMapBlock) map;
        int valuePosition = mapBlock.seekKeyExact((Block) key);
        if (valuePosition == -1) {
            throw missingKeyExceptionFactory.create(session, key);
        }
        return readNativeValue(valueType, mapBlock, valuePosition);
    }