presto-hive/src/main/java/io/prestosql/plugin/hive/HivePageSourceProvider.java/ColumnMapping/toColumnHandles
class ColumnMapping:        public static List<HiveColumnHandle> toColumnHandles(List<ColumnMapping> regularColumnMappings, boolean doCoercion, TypeManager typeManager)
        {
            return regularColumnMappings.stream()
                    .map(columnMapping -> {
                        HiveColumnHandle columnHandle = columnMapping.getHiveColumnHandle();
                        if (!doCoercion || !columnMapping.getCoercionFrom().isPresent()) {
                            return columnHandle;
                        }
                        return new HiveColumnHandle(
                                columnHandle.getName(),
                                columnMapping.getCoercionFrom().get(),
                                columnMapping.getCoercionFrom().get().getType(typeManager),
                                columnHandle.getHiveColumnIndex(),
                                columnHandle.getColumnType(),
                                Optional.empty());
                    })
                    .collect(toList());
        }