Empty Matriculation Update results in timeout

[bastihav]

Describe the bug Empty matriculation update results in akka timeout

{
    "name": "akka.pattern.AskTimeoutException: Ask timed out on [EntityRef(EntityTypeKey[de.upb.cs.uc4.hyperledger.commands.HyperledgerCommand](uc4matriculation), matriculation)] after [15000 ms]. Message of type [de.upb.cs.uc4.matriculation.impl.commands.AddEntriesToMatriculationData]. A typical reason for `AskTimeoutException` is that the recipient actor didn't send a reply.",
    "detail": "akka.pattern.AskTimeoutException: Ask timed out on [EntityRef(EntityTypeKey[de.upb.cs.uc4.hyperledger.commands.HyperledgerCommand](uc4matriculation), matriculation)] after [15000 ms]. Message of type [de.upb.cs.uc4.matriculation.impl.commands.AddEntriesToMatriculationData]. A typical reason for `AskTimeoutException` is that the recipient actor didn't send a reply.\n\tat akka.pattern.PromiseActorRef$.$anonfun$defaultOnTimeout$1(AskSupport.scala:646)\n\tat akka.pattern.PromiseActorRef$.$anonfun$apply$1(AskSupport.scala:667)\n\tat akka.actor.Scheduler$$anon$7.run(Scheduler.scala:476)\n\tat scala.concurrent.ExecutionContext$parasitic$.execute(ExecutionContext.scala:164)\n\tat akka.actor.LightArrayRevolverScheduler$TaskHolder.executeTask(LightArrayRevolverScheduler.scala:355)\n\tat akka.actor.LightArrayRevolverScheduler$$anon$3.executeBucket$1(LightArrayRevolverScheduler.scala:306)\n\tat akka.actor.LightArrayRevolverScheduler$$anon$3.nextTick(LightArrayRevolverScheduler.scala:310)\n\tat akka.actor.LightArrayRevolverScheduler$$anon$3.run(LightArrayRevolverScheduler.scala:262)\n\tat java.lang.Thread.run(Thread.java:748)\n"
}

To Reproduce PUT https://uc4.cs.upb.de/api/experimental/matriculation-management/student

{
  "matriculation": [
  ]
}

or

{
  "matriculation": [
    {
      "fieldOfStudy": "Mathematics",
      "semesters": [
      ]
    }
  ]
}

Expected behavior Should be 200/201 or some new error