SPIGOT-178: Treat ItemStacks of 0 size as empty

By: Thinkofdeath <thinkofdeath@spigotmc.org>

paper-server/nms-patches/Slot.patch

@@ -0,0 +1,12 @@
+--- ../work/decompile-8eb82bde//net/minecraft/server/Slot.java	2015-01-04 21:48:34.213601099 +0000
++++ src/main/java/net/minecraft/server/Slot.java	2015-01-04 21:48:34.213601099 +0000
+@@ -45,6 +45,9 @@
+     }
+ 
+     public boolean hasItem() {
++        if (getItem() != null && getItem().count == 0) {
++            set(null);
++        }
+         return this.getItem() != null;
+     }
+