WARNING: Failed to initialize a channel. Closing: [id: 0x21b225da]
java.lang.IllegalArgumentException: handler
    at com.google.common.base.Preconditions.checkArgument(Preconditions.java:122)
    at net.md_5.bungee.netty.HandlerBoss.setHandler(HandlerBoss.java:33)
    at protocolsupport.injector.BungeeNettyChannelInjector$CustomHandlerBoss.setHandler(BungeeNettyChannelInjector.java:92)
    at protocolsupport.injector.BungeeNettyChannelInjector$CustomHandlerBoss.<init>(BungeeNettyChannelInjector.java:86)
    at protocolsupport.injector.BungeeNettyChannelInjector$ChannelInitializerEntryPoint.initChannel(BungeeNettyChannelInjector.java:50)
    at protocolsupport.utils.netty.ChannelInitializer.channelRegistered(ChannelInitializer.java:17)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRegistered(AbstractChannelHandlerContext.java:149)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRegistered(AbstractChannelHandlerContext.java:135)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRegistered(AbstractChannelHandlerContext.java:128)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRegistered(DefaultChannelPipeline.java:1407)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRegistered(AbstractChannelHandlerContext.java:149)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRegistered(AbstractChannelHandlerContext.java:135)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRegistered(DefaultChannelPipeline.java:859)
    at io.netty.channel.AbstractChannel$AbstractUnsafe.register0(AbstractChannel.java:513)
    at io.netty.channel.AbstractChannel$AbstractUnsafe.access$200(AbstractChannel.java:423)
    at io.netty.channel.AbstractChannel$AbstractUnsafe$1.run(AbstractChannel.java:482)
    at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404)
    at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:313)
    at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
    at java.lang.Thread.run(Thread.java:748)