sbt -mem 1024 on the v1.8.222 tag mentions java 9?

[f1-outsourcing]

build manual states java 1.8+, but here an error is reported related to java 9?

[warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.
[info] Compiling 21 Scala sources to /home/software/marathon2/type-generator/target/scala-2.12/sbt-1.0/classes ...
[error] -release is only supported on Java 9 and higher
[warn] /home/software/marathon2/type-generator/src/main/scala/mesosphere/raml/backend/liquid/Filters.scala:14:26: non-variable type argument String in type pattern Iterable[String] is unchecked since it is eliminated by erasure
[warn]       case it: java.lang.Iterable[String] => it.asScala.map(_.toUpperCase).asJava
[warn]                          ^
[warn] /home/software/marathon2/type-generator/src/main/scala/mesosphere/raml/backend/liquid/Filters.scala:25:26: non-variable type argument String in type pattern Iterable[String] is unchecked since it is eliminated by erasure
[warn]       case it: java.lang.Iterable[String] => it.asScala.map(_.toLowerCase).asJava
[warn]                          ^
[warn] two warnings found


...
...
[info] Compiling 611 Scala sources and 9 Java sources to /home/software/marathon2/target/scala-2.12/classes ...
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/MarathonSchedulerActor.scala:408:12: a pure expression does nothing in statement posit
ion; multiline expressions might require enclosing parentheses
[warn]       await(Future.sequence(changeGoalsFuture))
[warn]            ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/MarathonSchedulerActor.scala:409:12: a pure expression does nothing in statement posit
ion; multiline expressions might require enclosing parentheses
[warn]       await(instancesAreTerminal)
[warn]            ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/api/v2/AppTasksResource.scala:49:11: [AssigningOptionToNull] You probably meant None,
not null.
[warn]     async {
[warn]           ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/api/v2/LeaderResource.scala:65:14: a pure expression does nothing in statement positio
n; multiline expressions might require enclosing parentheses
[warn]         await(runtimeConfigRepo.store(RuntimeConfiguration(backup, restore)))
[warn]              ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/api/v2/PodsResource.scala:89:20: local val identity in method apply is never used
[warn]       implicit val identity = await(authenticatedAsync(req))
[warn]                    ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/core/health/impl/HealthCheckWorker.scala:33:18: local val system in method run is neve
r used
[warn]     implicit val system = mat.system
[warn]                  ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/core/health/impl/HealthCheckWorker.scala:112:25: parameter value mat in method tcp is never used
[warn]     port: Int)(implicit mat: ActorMaterializer): Future[HealthResult] = {
[warn]                         ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/core/task/tracker/impl/InstanceTrackerActor.scala:172:24: This catches all Throwables. If this is really intended, use `case ex : Throwable` to clear this warning.
[warn]         } catch { case ex => InstanceUpdateEffect.Failure(ex) }
[warn]                        ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/raml/CheckConversion.scala:116:70: [PassPartialFunctionDirectly] You can pass the partial function in directly. (Remove `check => check match {`).
[warn]   implicit val checkRamlWriter: Writes[CoreCheck, AppCheck] = Writes { check =>
[warn]                                                                      ^
[warn] /home/software/marathon2/src/main/scala/mesosphere/marathon/raml/VolumeConversion.scala:144:95: [UseOptionFlatMapNotPatMatch] ... match { Some(x) => definedType match {
[warn]   case PersistentVolumeType.Root => scala.Some.apply[mesosphere.marathon.state.DiskType.Root.type](mesosphere.marathon.state.DiskType.Root)
[warn]   case PersistentVolumeType.Mount => scala.Some.apply[mesosphere.marathon.state.DiskType.Mount.type](mesosphere.marathon.state.DiskType.Mount)
[warn]   case PersistentVolumeType.Path => scala.Some.apply[mesosphere.marathon.state.DiskType.Path.type](mesosphere.marathon.state.DiskType.Path)
[warn] }; None => None} can be replaced with .flatMap(definedType match {
[warn]   case PersistentVolumeType.Root => scala.Some.apply[mesosphere.marathon.state.DiskType.Root.type](mesosphere.marathon.state.DiskType.Root)
[warn]   case PersistentVolumeType.Mount => scala.Some.apply[mesosphere.marathon.state.DiskType.Mount.type](mesosphere.marathon.state.DiskType.Mount)

[jeschkies]

Most of the logs you've posted ware warnings. What's the error message at the end of sbt clean compile?