[23:21:15] [Server thread/FATAL] [net.minecraft.server.MinecraftServer]: Error executing task
 java.util.concurrent.ExecutionException: java.lang.NoClassDefFoundError: net/minecraft/server/integrated/IntegratedServer
        at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_241]
        at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_241]
        at net.minecraft.util.Util.func_181617_a(SourceFile:47) [h.class:?]
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:926) [MinecraftServer.class:?]
        at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:461) [nz.class:?]
        at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:865) [MinecraftServer.class:?]
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:737) [MinecraftServer.class:?]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_241]
Caused by: java.lang.NoClassDefFoundError: net/minecraft/server/integrated/IntegratedServer
        at fr.militario.spacex.entity.EntityFalcon9Rocket.func_184199_a(EntityFalcon9Rocket.java:118) ~[EntityFalcon9Rocket.class:?]
        at net.minecraft.network.NetHandlerPlayServer.func_147340_a(NetHandlerPlayServer.java:1827) ~[pa.class:?]
        at net.minecraft.network.play.client.CPacketUseEntity.func_148833_a(SourceFile:69) ~[li.class:?]
        at net.minecraft.network.play.client.CPacketUseEntity.func_148833_a(SourceFile:13) ~[li.class:?]
        at net.minecraft.network.PacketThreadUtil.lambda$checkThreadAndEnqueue$0(PacketThreadUtil.java:14) ~[hv.class:?]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_241]
        at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_241]
        at net.minecraft.util.Util.func_181617_a(SourceFile:46) ~[h.class:?]
        ... 5 more
Caused by: java.lang.ClassNotFoundException: net.minecraft.server.integrated.IntegratedServer



java.lang.NullPointerException: Ticking entity
	at fr.militario.spacex.entity.EntityDragonCapsule.synchronizedUpdate(EntityDragonCapsule.java:439)
	at fr.militario.spacex.entity.EntityDragonCapsule.func_70071_h_(EntityDragonCapsule.java:468)
	at net.minecraft.world.World.func_72866_a(World.java:2340)
	at net.minecraft.world.World.func_72870_g(World.java:2294)
	at net.minecraft.world.World.func_72939_s(World.java:2076)
	at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:852)
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:988)
	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:461)
	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:865)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:737)
	at java.lang.Thread.run(Unknown Source)