From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Lukasz Derlatka <toranktto@gmail.com>
Date: Mon, 11 Nov 2019 16:08:13 +0100
Subject: [PATCH] Fix AssertionError when player hand set to empty type

Fixes an AssertionError when setting the player's item in hand to null or a new ItemStack of Air in PlayerInteractEvent
Fixes GH-2718

diff --git a/src/main/java/net/minecraft/server/EntityLiving.java b/src/main/java/net/minecraft/server/EntityLiving.java
index d354e9b504b6872f20a9e433522827589bd4778a..12b27c44d77b72fa4a4d42cfe3db8394a47d9c9b 100644
--- a/src/main/java/net/minecraft/server/EntityLiving.java
+++ b/src/main/java/net/minecraft/server/EntityLiving.java
@@ -2040,6 +2040,7 @@ public abstract class EntityLiving extends Entity {
         return predicate.test(this.getItemInMainHand().getItem()) || predicate.test(this.getItemInOffHand().getItem());
     }
 
+    public final ItemStack getItemInHand(EnumHand enumhand) { return this.b(enumhand); } // Paper - OBFHELPER
     public ItemStack b(EnumHand enumhand) {
         if (enumhand == EnumHand.MAIN_HAND) {
             return this.getEquipment(EnumItemSlot.MAINHAND);
diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
index a396051c46613ac863fd296b55465c01bd2c7ce7..dc7d0f902aa0f2601656cd5e9e434c276111a7d4 100644
--- a/src/main/java/net/minecraft/server/PlayerConnection.java
+++ b/src/main/java/net/minecraft/server/PlayerConnection.java
@@ -1478,6 +1478,10 @@ public class PlayerConnection implements PacketListenerPlayIn {
                 this.player.getBukkitEntity().updateInventory(); // SPIGOT-2524
                 return;
             }
+            // Paper start
+            itemstack = this.player.getItemInHand(enumhand);
+            if (itemstack.isEmpty()) return;
+            // Paper end
             EnumInteractionResult enuminteractionresult = this.player.playerInteractManager.a(this.player, worldserver, itemstack, enumhand);
 
             if (enuminteractionresult.b()) {