Vaadin 8 compiled with JDK 11 produces question marks for negative sizes in .css

Hi,

I stumbled upon this issue and noticed there was a forum post about it as well: Valo theme on Vaadin 8 compiled using jdk11 produces question marks for neg - Flow -

So after switching from compiling with JDK 8 to JDK 11 the .sass compilation can’t handle negative sizes correctly, but instead changes them to question marks. In the forum post there is a mention about using a “-release” parameter, but I can’t find any documentation about this.

Is there any way of fixing this?

Thanks in advance!