PaperMC/paper-server/nms-patches/net/minecraft/world/inventory/ContainerMerchant.patch

--- a/net/minecraft/world/inventory/ContainerMerchant.java
+++ b/net/minecraft/world/inventory/ContainerMerchant.java
@@ -12,6 +12,8 @@
 import net.minecraft.world.item.trading.MerchantRecipe;
 import net.minecraft.world.item.trading.MerchantRecipeList;
 
+import org.bukkit.craftbukkit.inventory.CraftInventoryView; // CraftBukkit
+
 public class ContainerMerchant extends Container {
 
     protected static final int PAYMENT1_SLOT = 0;
@@ -31,6 +33,19 @@
     private boolean showProgressBar;
     private boolean canRestock;
 
+    // CraftBukkit start
+    private CraftInventoryView bukkitEntity = null;
+    private PlayerInventory player;
+
+    @Override
+    public CraftInventoryView getBukkitView() {
+        if (bukkitEntity == null) {
+            bukkitEntity = new CraftInventoryView(this.player.player.getBukkitEntity(), new org.bukkit.craftbukkit.inventory.CraftInventoryMerchant(trader, tradeContainer), this);
+        }
+        return bukkitEntity;
+    }
+    // CraftBukkit end
+
     public ContainerMerchant(int i, PlayerInventory playerinventory) {
         this(i, playerinventory, new MerchantWrapper(playerinventory.player));
     }
@@ -42,6 +57,7 @@
         this.a(new Slot(this.tradeContainer, 0, 136, 37));
         this.a(new Slot(this.tradeContainer, 1, 162, 37));
         this.a((Slot) (new SlotMerchantResult(playerinventory.player, imerchant, this.tradeContainer, 2, 220, 37)));
+        this.player = playerinventory; // CraftBukkit - save player
 
         int j;
 
@@ -154,7 +170,7 @@
     }
 
     private void o() {
-        if (!this.trader.getWorld().isClientSide) {
+        if (!this.trader.getWorld().isClientSide && this.trader instanceof Entity) { // CraftBukkit - SPIGOT-5035
             Entity entity = (Entity) this.trader;
 
             this.trader.getWorld().a(entity.locX(), entity.locY(), entity.locZ(), this.trader.getTradeSound(), SoundCategory.NEUTRAL, 1.0F, 1.0F, false);