create a file that looks like this:
const template = `
webgrease chokes on it which makes bundler choke on it which makes your site unable to respond to any requests.
It is very very common in both react and angular to use multiline templates I'm frankly shocked that this has not been reported yet.
The only available workaround is to not use multiline string templates at all. This breaks even when in debug mode when webgrease shouldn't even be involved!