Paper/patches/server/0521-Do-not-crash-from-invalid-ingredient-lists-in-Villag.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Sun, 27 Dec 2020 11:31:06 +0000
Subject: [PATCH] Do not crash from invalid ingredient lists in
 VillagerAcquireTradeEvent


diff --git a/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java b/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java
index 49bc867f189b0d4c236a47670676cc67920c2cd7..e7dda8959eb92c069af001126aafc759e7e7d2de 100644
--- a/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java
+++ b/src/main/java/net/minecraft/world/entity/npc/AbstractVillager.java
@@ -275,7 +275,11 @@ public abstract class AbstractVillager extends AgeableMob implements InventoryCa
                     Bukkit.getPluginManager().callEvent(event);
                 }
                 if (!event.isCancelled()) {
-                    recipeList.add(CraftMerchantRecipe.fromBukkit(event.getRecipe()).toMinecraft());
+                    // Paper start
+                    final CraftMerchantRecipe craftMerchantRecipe = CraftMerchantRecipe.fromBukkit(event.getRecipe());
+                    if (craftMerchantRecipe.getIngredients().isEmpty()) return;
+                    recipeList.add(craftMerchantRecipe.toMinecraft());
+                    // Paper end
                 }
                 // CraftBukkit end
             }