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/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index 0de98ce5db144d0b5cde34f62991c46b7aedad8b..f961a0f5b571d86c8d2b57f489b421fbfb01ca3d 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -1753,6 +1753,10 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Ser
                 this.player.getBukkitEntity().updateInventory(); // SPIGOT-2524
                 return;
             }
+            // Paper start
+            itemstack = this.player.getItemInHand(enumhand);
+            if (itemstack.isEmpty()) return;
+            // Paper end
             InteractionResult enuminteractionresult = this.player.gameMode.useItem(this.player, worldserver, itemstack, enumhand);
 
             if (enuminteractionresult.shouldSwing()) {