[Webpack] Module not found: Error: Empty dependency (no request) fix

If you have these errors in Webpack (encore):
This dependency was not found:

*  in ./node_modules/css-loader??ref--1-2!./src/AppBundle/Resources/public/css/styles.css

or:

Module build failed: ModuleNotFoundError: Module not found: Error: Empty dependency (no request)
   at factoryCallback (/var/www/project/core/node_modules/webpack/lib/Compilation.js:282:40)

It because you have background-image("") without an url. Add it or remove this attribute.