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java.lang.IllegalArgumentException: Comparison method violates its general contract!	at java.util.TimSort.mergeHi(Unknown Source)	at java.util.TimSort.mergeAt(Unknown Source)	at java.util.TimSort.mergeForceCollapse(Unknown Source)	at java.util.TimSort.sort(Unknown Source)	at java.util.Arrays.sort(Unknown Source)	at java.util.stream.SortedOps$SizedRefSortingSink.end(Unknown Source)	at java.util.stream.AbstractPipeline.copyInto(Unknown Source)	at java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(Unknown Source)	at java.util.stream.AbstractPipeline.evaluate(Unknown Source)	at java.util.stream.ReferencePipeline.collect(Unknown Source)	at net.sf.freecol.common.util.CollectionUtils.sort_internal(CollectionUtils.java:1986)	at net.sf.freecol.common.util.CollectionUtils.sort(CollectionUtils.java:1933)	at net.sf.freecol.server.ai.AIMain.writeChildren(AIMain.java:491)	at net.sf.freecol.common.model.FreeColObject.toXML(FreeColObject.java:1015)	at net.sf.freecol.common.model.FreeColObject.toXML(FreeColObject.java:991)	at net.sf.freecol.server.FreeColServer.saveGame(FreeColServer.java:863)	at net.sf.freecol.server.FreeColServer.saveGame(FreeColServer.java:767)	at net.sf.freecol.client.control.InGameController.saveGame(InGameController.java:589)	at net.sf.freecol.client.control.InGameController.autoSaveGame(InGameController.java:573)	at net.sf.freecol.client.control.InGameController.setCurrentPlayer(InGameController.java:4691)	at net.sf.freecol.client.control.InGameInputHandler.setCurrentPlayer(InGameInputHandler.java:1039)	at net.sf.freecol.client.control.InGameInputHandler.lambda$new$34(InGameInputHandler.java:190)	at net.sf.freecol.client.control.ClientInputHandler.handle(ClientInputHandler.java:129)	at net.sf.freecol.client.control.InGameInputHandler.handle(InGameInputHandler.java:289)	at net.sf.freecol.common.networking.DOMMessage.handleList(DOMMessage.java:401)	at net.sf.freecol.common.networking.MultipleMessage.applyHandler(MultipleMessage.java:107)	at net.sf.freecol.client.control.InGameInputHandler.multiple(InGameInputHandler.java:875)	at net.sf.freecol.client.control.InGameInputHandler.lambda$new$23(InGameInputHandler.java:168)	at net.sf.freecol.client.control.ClientInputHandler.handle(ClientInputHandler.java:129)	at net.sf.freecol.client.control.InGameInputHandler.handle(InGameInputHandler.java:289)	at net.sf.freecol.common.networking.Connection.handle(Connection.java:541)	at net.sf.freecol.common.networking.Connection.handleQuery(Connection.java:512)	at net.sf.freecol.common.networking.ReceivingThread$1.run(ReceivingThread.java:331)