new line inserted at start for every response when MopaBootstrapBundle included with Symfony 4

[PaddyLock]

It took me a while to track down the source of this issue, but I was getting a new blank line at the start of every response returned, even debug error pages and JSON responses. I narrowed it down to including the MopaBootstrapBundle. I am using Symfony 4.1. If I edit the file Mopa\Bundle\BootstrapBundle\MopaBootstrapBundle and comment out the line

use Symfony\Component\HttpKernel\Bundle\Bundle;

and remove extends Bundle then the blank line disappears. However, this is the only bundle this affects, so I'm not sure where the actual error is happening. At the moment this bundle is unusable with Symfony 4.