public static List<Recipe> getCatRecipes(IJeiHelpers helper, int var) {
        List<Recipe> jeiRecipes = new ArrayList<>();

        List<RecipeCatExkva> recipes = new ArrayList<>();

        switch (var) {
            case 7 : recipes = Exkva.METAL_FORMER_RECIPES;
        }

        for(RecipeCatExkva recipe : recipes) {

            List<ItemStack> cat = Arrays.asList(recipe.getCat());
            List<ItemStack> input = Arrays.asList(recipe.getStackInput());
            input.addAll(cat);
            List<ItemStack> output = Arrays.asList(recipe.getOutput());

            jeiRecipes.add(new Recipe(input, output));
        }

        return jeiRecipes;
    }

[21:28:47] [main/ERROR] [jei]: Failed to register mod plugin: class exokem.exkva.jei.ExkvaPlugin
java.lang.UnsupportedOperationException: null
    at java.util.AbstractList.add(AbstractList.java:148) ~[?:1.8.0_181]
    at java.util.AbstractList.add(AbstractList.java:108) ~[?:1.8.0_181]
    at java.util.AbstractCollection.addAll(AbstractCollection.java:344) ~[?:1.8.0_181]
    at exokem.exkva.jei.base.RecipeMaker.getCatRecipes(RecipeMaker.java:130) ~[RecipeMaker.class:?]
    at exokem.exkva.jei.ExkvaPlugin.register(ExkvaPlugin.java:41) ~[ExkvaPlugin.class:?]
    at mezz.jei.startup.JeiStarter.registerPlugins(JeiStarter.java:181) [JeiStarter.class:?]
    at mezz.jei.startup.JeiStarter.start(JeiStarter.java:64) [JeiStarter.class:?]
    at mezz.jei.startup.ProxyCommonClient.loadComplete(ProxyCommonClient.java:120) [ProxyCommonClient.class:?]
    at mezz.jei.JustEnoughItems.loadComplete(JustEnoughItems.java:54) [JustEnoughItems.class:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181]
    at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:626) [FMLModContainer.class:?]
    at sun.reflect.GeneratedMethodAccessor11.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181]
    at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91) [guava-21.0.jar:?]
    at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150) [guava-21.0.jar:?]
    at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76) [guava-21.0.jar:?]
    at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399) [guava-21.0.jar:?]
    at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71) [guava-21.0.jar:?]
    at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116) [guava-21.0.jar:?]
    at com.google.common.eventbus.EventBus.post(EventBus.java:217) [guava-21.0.jar:?]
    at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:218) [LoadController.class:?]
    at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:196) [LoadController.class:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181]
    at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91) [guava-21.0.jar:?]
    at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150) [guava-21.0.jar:?]
    at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76) [guava-21.0.jar:?]
    at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399) [guava-21.0.jar:?]
    at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71) [guava-21.0.jar:?]
    at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116) [guava-21.0.jar:?]
    at com.google.common.eventbus.EventBus.post(EventBus.java:217) [guava-21.0.jar:?]
    at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:135) [LoadController.class:?]
    at net.minecraftforge.fml.common.Loader.initializeMods(Loader.java:752) [Loader.class:?]
    at net.minecraftforge.fml.client.FMLClientHandler.finishMinecraftLoading(FMLClientHandler.java:336) [FMLClientHandler.class:?]
    at net.minecraft.client.Minecraft.init(Minecraft.java:581) [Minecraft.class:?]
    at net.minecraft.client.Minecraft.run(Minecraft.java:421) [Minecraft.class:?]
    at net.minecraft.client.main.Main.main(Main.java:118) [Main.class:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181]
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) [launchwrapper-1.12.jar:?]
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181]
    at net.minecraftforge.gradle.GradleStartCommon.launch(GradleStartCommon.java:97) [start/:?]
    at GradleStart.main(GradleStart.java:25) [start/:?]