Removing Rockets throws error

[lapplislazuli]

Description
There occurs an error when a rocket is removed without collision.

Error Message
Exception in thread "JavaFX Application Thread" java.util.ConcurrentModificationException at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:966) at java.util.LinkedList$ListItr.next(LinkedList.java:888) at space.core.SpaceObject.update(SpaceObject.java:43) at space.shuttle.SpaceShuttle.update(SpaceShuttle.java:72) at space.shuttle.ArmedSpaceShuttle.update(ArmedSpaceShuttle.java:30) at space.core.SpaceObject.update(SpaceObject.java:45) at space.core.SpaceObject.update(SpaceObject.java:45) at logic.manager.UpdateManager.update(UpdateManager.java:52) at logic.manager.UpdateManager$1.lambda$0(UpdateManager.java:68) at com.sun.javafx.application.PlatformImpl.lambda$null$174(PlatformImpl.java:295) at java.security.AccessController.doPrivileged(Native Method) at com.sun.javafx.application.PlatformImpl.lambda$runLater$175(PlatformImpl.java:294) at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95) at com.sun.glass.ui.win.WinApplication._runLoop(Native Method) at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191) at java.lang.Thread.run(Thread.java:745)

Reproduction

1. Start the Game
2. Shoot somewhere without collision
3. See Console

This occurs in every branch

Expected behavior
The Items should not cause any error.
Its strange that a collision stops this error from happening.