Error in system.log when exporting product feed

[LucasMDL]

When exporting an product feed in de admin panel, we get the following error in the system.log:

Warning: Cannot modify header information - headers already sent by (output started at vendor/lengow/module-connector/Model/Export/Feed.php:423) in vendor/magento/framework/Stdlib/Cookie/PhpCookieManager.php on line 152