Description: Exception in server tick loop

java.lang.NoClassDefFoundError: cn/academy/entity/EntityRailgunFX
at cn.nulladev.exac.core.EXACItems.(EXACItems.java:19)
at cn.nulladev.exac.core.EXACRegistry.addItems(EXACRegistry.java:87)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_52_EXACRegistry_addItems_Register.invoke(.dynamic)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
at net.minecraftforge.fml.common.eventhandler.EventBus$1.invoke(EventBus.java:146)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:190)
at net.minecraftforge.registries.GameData.fireRegistryEvents(GameData.java:858)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:630)
at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:98)
at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:335)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:167)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:603)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: cn.academy.entity.EntityRailgunFX
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 13 more
Caused by: net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerException: Exception in class transformer net.minecraftforge.fml.common.asm.transformers.SideTransformer@2e115a55 from coremod FMLCorePlugin
at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:262)
at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176)
... 15 more
Caused by: java.lang.RuntimeException: Attempted to load class cn/academy/entity/EntityRailgunFX for invalid side SERVER
at net.minecraftforge.fml.common.asm.transformers.SideTransformer.transform(SideTransformer.java:62)
at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:258)
... 17 more

solved