My server has repeatedly crashes
It was captured for the first time before the crash statistics

Current Thread: Server thread
PID: 21 | Suspended: false | Native: false | State: RUNNABLE
Stack:
net.minecraft.server.v1_9_R1.WorldServer.a(WorldServer.java:776)
net.minecraft.server.v1_9_R1.WorldServer.a(WorldServer.java:761)
net.minecraft.server.v1_9_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:283)
net.minecraft.server.v1_9_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:130)
net.minecraft.server.v1_9_R1.ChunkProviderServer.saveChunk(ChunkProviderServer.java:240)
net.minecraft.server.v1_9_R1.ChunkProviderServer.unloadChunks(ChunkProviderServer.java:294)
net.minecraft.server.v1_9_R1.WorldServer.doTick(WorldServer.java:230)
net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:776)
net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:400)
net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:660)
net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:559)
java.lang.Thread.run(Thread.java:745)