NPE - Cannot invoke "org.bukkit.inventory.ItemStack.isSimilar(org.bukkit.inventory.ItemStack)" because "t" is null

[StrangeOne101]

Stacktrace

[20:57:00 ERROR]: Could not pass event InventoryClickEvent to ProjectKorraItems v2.0
java.lang.NullPointerException: Cannot invoke "org.bukkit.inventory.ItemStack.isSimilar(org.bukkit.inventory.ItemStack)" because "t" is null
        at org.bukkit.inventory.RecipeChoice$ExactChoice.test(RecipeChoice.java:200) ~[paper-api-1.18.2-R0.1-SNAPSHOT.jar:?]
        at com.strangeone101.holoitemsapi.recipe.RecipeManager.sendRecipes(RecipeManager.java:101) ~[ProjectKorraItems-2.0-PK1.9.3.jar:?]
        at com.strangeone101.holoitemsapi.listener.ItemListener.onTakeItem(ItemListener.java:532) ~[ProjectKorraItems-2.0-PK1.9.3.jar:?]