Running "fix" on an empty module fails

[HilcoWijbenga]

A project with just this build.mill (using Mill 0.12.2) dies on ./mill __.fix.

package build

import $ivy.`com.goyeau::mill-scalafix::0.4.2`
import com.goyeau.mill.scalafix.ScalafixModule
import mill.scalalib.SbtModule

object main extends SbtModule with ScalafixModule {
    def scalaVersion = "2.13.15"
}

It might seem strange not to have any sources in a module but I have a couple of "aggregation" modules that simply list other modules that they depend on. This used to work fine (pre 0.12).

Adding a single source file makes the problem go away ... but then I have a useless source file. :-)