Error after Fill command

[HomeLandingsDE]

04.07 22:09:10 [Server] Server thread/WARN [WorldBorder] Task #243440 for WorldBorder v1.9.10 (beta) generated an exception
04.07 22:09:10 [Server] INFO java.util.ConcurrentModificationException: null
04.07 22:09:10 [Server] INFO at java.util.HashMap$HashIterator.nextNode(Unknown Source) ~[?:1.8.0_161]
04.07 22:09:10 [Server] INFO at java.util.HashMap$KeyIterator.next(Unknown Source) ~[?:1.8.0_161]
04.07 22:09:10 [Server] INFO at java.lang.Iterable.forEach(Unknown Source) ~[?:1.8.0_161]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.ChunkMapDistance.a(SourceFile:132) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.ChunkProviderServer.tickDistanceManager(ChunkProviderServer.java:204) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.ChunkProviderServer.getChunkFutureMainThread(ChunkProviderServer.java:144) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:91) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.World.getChunkAt(World.java:212) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.IWorldReader.getChunkAt(SourceFile:105) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.World.getChunkAt(World.java:207) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.WorldServer.setForceLoaded(WorldServer.java:1444) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at org.bukkit.craftbukkit.v1_14_R1.CraftWorld.setChunkForceLoaded(CraftWorld.java:485) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at com.wimbli.WorldBorder.WorldFillTask.run(WorldFillTask.java:318) ~[?:?]
04.07 22:09:10 [Server] INFO at org.bukkit.craftbukkit.v1_14_R1.scheduler.CraftTask.run(CraftTask.java:81) ~[spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at org.bukkit.craftbukkit.v1_14_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:394) [spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.b(MinecraftServer.java:1008) [spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.DedicatedServer.b(DedicatedServer.java:396) [spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.a(MinecraftServer.java:956) [spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at net.minecraft.server.v1_14_R1.MinecraftServer.run(MinecraftServer.java:801) [spigot-1.14.2.jar:git-Spigot-093165d-ba575a5]
04.07 22:09:10 [Server] INFO at java.lang.Thread.run(Unknown Source) [?:1.8.0_161]