MCSkill Tree Crash Log Server

[Server thread/ERROR] [FML]: An error occurred trying to load a proxy into zdoctor.mcskilltree.ModMain.proxy
java.lang.InstantiationException: null
        at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(Unknown Source) ~[?:1.8.0_221]
        at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[?:1.8.0_221]
        at java.lang.Class.newInstance(Unknown Source) ~[?:1.8.0_221]
        at net.minecraftforge.fml.common.ProxyInjector.inject(ProxyInjector.java:85) [ProxyInjector.class:?]
        at net.minecraftforge.fml.common.FMLModContainer.constructMod(FMLModContainer.java:611) [FMLModContainer.class:?]
        at sun.reflect.GeneratedMethodAccessor10.invoke(Unknown Source) ~[?:?]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_221]
        at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_221]
        at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76) [minecraft_server.1.12.2.jar:?]
        at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.EventBus.post(EventBus.java:217) [minecraft_server.1.12.2.jar:?]
        at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:219) [LoadController.class:?]
        at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:197) [LoadController.class:?]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_221]
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_221]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_221]
        at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_221]
        at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76) [minecraft_server.1.12.2.jar:?]
        at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116) [minecraft_server.1.12.2.jar:?]
        at com.google.common.eventbus.EventBus.post(EventBus.java:217) [minecraft_server.1.12.2.jar:?]
        at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:136) [LoadController.class:?]
        at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:593) [Loader.class:?]
        at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:98) [FMLServerHandler.class:?]
        at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:333) [FMLCommonHandler.class:?]
        at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:125) [nz.class:?]
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486) [MinecraftServer.class:?]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_221]