I get this in my logs every time I try to use the better foliage mod. I don't understand what am I doing wrong?

[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: java.lang.reflect.InvocationTargetException
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at java.lang.reflect.Method.invoke(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:196)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:231)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at org.multimc.EntryPoint.listen(EntryPoint.java:143)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launch:231]: at org.multimc.EntryPoint.main(EntryPoint.java:34)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: Caused by: java.lang.NoClassDefFoundError: kotlin/reflect/KDeclarationContainer
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at mods.betterfoliage.loader.Refs.(Refs.kt:13)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at mods.betterfoliage.loader.BetterFoliageTransformer.(BetterFoliageCore.kt:13)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at java.lang.reflect.Constructor.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at java.lang.Class.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.(ASMTransformerWrapper.java:243)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at $wrapper.mods.betterfoliage.loader.BetterFoliageTransformer.(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at java.lang.reflect.Constructor.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at java.lang.Class.newInstance(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at net.minecraft.launchwrapper.LaunchClassLoader.registerTransformer(LaunchClassLoader.java:88)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at net.minecraftforge.fml.relauncher.CoreModManager$FMLPluginWrapper.injectIntoClassLoader(CoreModManager.java:132)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at net.minecraft.launchwrapper.Launch.launch(Launch.java:115)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
[21:34:05] [main/INFO] [STDERR]: [org.multimc.onesix.OneSixLauncher:launchWithMainClass:200]: ... 8 more
[21:34:05] [main/INFO] [STDERR]: [java.lang.Throwable:printStackTrace:-1]: Caused by: java.lang.ClassNotFoundException: kotlin.reflect.KDeclarationContainer
[21:34:05] [main/INFO] [STDERR]: [java.lang.Throwable:printStackTrace:-1]: at java.net.URLClassLoader.findClass(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [java.lang.Throwable:printStackTrace:-1]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:117)
[21:34:05] [main/INFO] [STDERR]: [java.lang.Throwable:printStackTrace:-1]: at java.lang.ClassLoader.loadClass(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [java.lang.Throwable:printStackTrace:-1]: at java.lang.ClassLoader.loadClass(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [java.lang.Throwable:printStackTrace:-1]: ... 26 more
[21:34:05] [main/INFO] [STDOUT]: [org.multimc.EntryPoint:main:37]: Exiting with -1
[21:34:05] [main/INFO] [STDERR]: [java.lang.ThreadGroup:uncaughtException:-1]: net.minecraftforge.fml.relauncher.FMLSecurityManager$ExitTrappedException
[21:34:05] [main/INFO] [STDERR]: [java.lang.ThreadGroup:uncaughtException:-1]: at net.minecraftforge.fml.relauncher.FMLSecurityManager.checkPermission(FMLSecurityManager.java:49)
[21:34:05] [main/INFO] [STDERR]: [java.lang.ThreadGroup:uncaughtException:-1]: at java.lang.SecurityManager.checkExit(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [java.lang.ThreadGroup:uncaughtException:-1]: at java.lang.Runtime.exit(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [java.lang.ThreadGroup:uncaughtException:-1]: at java.lang.System.exit(Unknown Source)
[21:34:05] [main/INFO] [STDERR]: [java.lang.ThreadGroup:uncaughtException:-1]: at org.multimc.EntryPoint.main(EntryPoint.java:38)
Exception in thread "main"