`sbt compile` fails on sbt.internal.inc.MappedVirtualFile (but works on sbt 1.3.x)

[codesurf42]

When I am trying to compile this project, it fails with

[error] java.lang.ClassCastException: class sbt.internal.inc.MappedVirtualFile cannot be cast to class java.io.File (sbt.internal.inc.MappedVirtualFile is in unnamed module of loader sbt.internal.MetaBuildLoader @587e5365; java.io.File is in module java.base of loader 'bootstrap')
[error]         at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:285)
[error]         at scala.collection.Iterator.foreach(Iterator.scala:943)
[error]         at scala.collection.Iterator.foreach$(Iterator.scala:943)
[error]         at scala.collection.AbstractIterator.foreach(Iterator.scala:1431)
[error]         at scala.collection.IterableLike.foreach(IterableLike.scala:74)
[error]         at scala.collection.IterableLike.foreach$(IterableLike.scala:73)
[error]         at scala.collection.AbstractIterable.foreach(Iterable.scala:56)
[error]         at scala.collection.TraversableLike.map(TraversableLike.scala:285)
[error]         at scala.collection.TraversableLike.map$(TraversableLike.scala:278)
[error]         at scala.collection.AbstractTraversable.map(Traversable.scala:108)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.$anonfun$generateExercisesTask$13(ExerciseCompilerPlugin.scala:214)
[error]         at cats.syntax.EitherObjectOps$.catchNonFatal$extension(either.scala:338)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.invokeCompiler$1(ExerciseCompilerPlugin.scala:209)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.$anonfun$generateExercisesTask$33(ExerciseCompilerPlugin.scala:247)
[error]         at cats.instances.ListInstances$$anon$1.$anonfun$traverse$2(list.scala:78)
[error]         at cats.instances.ListInstances$$anon$1.loop$2(list.scala:68)
[error]         at cats.instances.ListInstances$$anon$1.$anonfun$foldRight$2(list.scala:70)
[error]         at cats.Eval$.advance(Eval.scala:271)
[error]         at cats.Eval$.loop$1(Eval.scala:350)
[error]         at cats.Eval$.cats$Eval$$evaluate(Eval.scala:368)
[error]         at cats.Eval$Defer.value(Eval.scala:257)
[error]         at cats.instances.ListInstances$$anon$1.traverse(list.scala:77)
[error]         at cats.instances.ListInstances$$anon$1.traverse(list.scala:16)
[error]         at cats.Traverse$Ops.traverse(Traverse.scala:19)
[error]         at cats.Traverse$Ops.traverse$(Traverse.scala:19)
[error]         at cats.Traverse$ToTraverseOps$$anon$2.traverse(Traverse.scala:19)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.$anonfun$generateExercisesTask$32(ExerciseCompilerPlugin.scala:247)
[error]         at scala.util.Either.flatMap(Either.scala:341)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.$anonfun$generateExercisesTask$30(ExerciseCompilerPlugin.scala:246)
[error]         at scala.util.Either.flatMap(Either.scala:341)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.$anonfun$generateExercisesTask$27(ExerciseCompilerPlugin.scala:243)
[error]         at scala.util.Either.flatMap(Either.scala:341)
[error]         at org.scalaexercises.plugin.sbtexercise.ExerciseCompilerPlugin$.$anonfun$generateExercisesTask$1(ExerciseCompilerPlugin.scala:240)
[error]         at scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error]         at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
[error]         at sbt.std.Transform$$anon$4.work(Transform.scala:68)
[error]         at sbt.Execute.$anonfun$submit$2(Execute.scala:282)
[error]         at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
[error]         at sbt.Execute.work(Execute.scala:291)
[error]         at sbt.Execute.$anonfun$submit$1(Execute.scala:282)
[error]         at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error]         at sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
[error]         at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error]         at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
[error]         at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error]         at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[error]         at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[error]         at java.base/java.lang.Thread.run(Thread.java:834)
[error] (Compile-generated-exercises / generateExercises) java.lang.ClassCastException: class sbt.internal.inc.MappedVirtualFile cannot be cast to class java.io.File (sbt.internal.inc.MappedVirtualFile is in unnamed module of loader sbt.internal.MetaBuildLoader @587e5365; java.io.File is in module java.base of loader 'bootstrap')
[error] Total time: 10 s, completed Feb 27, 2021, 9:47:18 PM```

However I can compile it with sbt 1.3.13