SWM Not working

[CommandCracker8]

Describe the issue
When starting my server, I get two errors. These are the errors I get:

javassist.NotFoundException: net.minecraft.server.v1_8_R3.WorldType
        at javassist.ClassPool.get(ClassPool.java:422)
        at javassist.bytecode.Descriptor.toCtClass(Descriptor.java:571)
        at javassist.bytecode.Descriptor.getParameterTypes(Descriptor.java:424)
        at javassist.CtBehavior.getParameterTypes(CtBehavior.java:323)
        at com.grinderwolf.swm.clsm.NMSTransformer.transform(NMSTransformer.java:157)
        at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
        at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        at org.bukkit.craftbukkit.Main.main(Main.java:201)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at com.destroystokyo.paperclip.Paperclip.main(Paperclip.java:177)

And

[11:50:25 WARN]: javassist.NotFoundException: org.bukkit.World
[11:50:25 WARN]:        at javassist.ClassPool.get(ClassPool.java:422)
[11:50:25 WARN]:        at javassist.bytecode.Descriptor.toCtClass(Descriptor.java:571)
[11:50:25 WARN]:        at javassist.bytecode.Descriptor.getParameterTypes(Descriptor.java:424)
[11:50:25 WARN]:        at javassist.CtBehavior.getParameterTypes(CtBehavior.java:323)
[11:50:25 WARN]:        at com.grinderwolf.swm.clsm.NMSTransformer.transform(NMSTransformer.java:157)
[11:50:25 WARN]:        at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
[11:50:25 WARN]:        at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
[11:50:25 WARN]:        at java.lang.ClassLoader.defineClass1(Native Method)
[11:50:25 WARN]:        at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
[11:50:25 WARN]:        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
[11:50:25 WARN]:        at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
[11:50:25 WARN]:        at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
[11:50:25 WARN]:        at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
[11:50:25 WARN]:        at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
[11:50:25 WARN]:        at java.security.AccessController.doPrivileged(Native Method)
[11:50:25 WARN]:        at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
[11:50:25 WARN]:        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
[11:50:25 WARN]:        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
[11:50:25 WARN]:        at net.minecraft.server.v1_8_R3.PlayerList.<init>(PlayerList.java:71)
[11:50:25 WARN]:        at net.minecraft.server.v1_8_R3.DedicatedPlayerList.<init>(SourceFile:14)
[11:50:25 WARN]:        at net.minecraft.server.v1_8_R3.DedicatedServer.init(DedicatedServer.java:176)
[11:50:25 WARN]:        at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:563)
[11:50:25 WARN]:        at java.lang.Thread.run(Thread.java:748)

Also, when I create a new world, it doesn't create a void world like it does in the video.
One final thing: When I try to create a new world, it does create it but also says it already exists.

Spigot version
It's Paper with version 1.8.8

Plugin version
2.2.1

How to reproduce
I don't know.

Crash reports (if available)
Does not crash.

[CommandCracker8]

Fixed.