Warning with -Xsource:2.14

[jhnsmth]

On Scala 2.13 with -Xsource:2.14 compiler option, newtype macro gives the following warning

Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method hashCode, 
or remove the empty argument list from its definition (Java-defined methods are exempt).
In Scala 3, an unapplied method like this will be eta-expanded into a function.

It makes newtypes unusable with both this option and -Xfatal-warnings enabled