#540: Add Inventory#isEmpty()

By: Parker Hawke <hawkeboyz2@hotmail.com>

paper-api/src/main/java/org/bukkit/inventory/Inventory.java

@@ -288,6 +288,14 @@ public interface Inventory extends Iterable<ItemStack> {
      */
     public int firstEmpty();
 
+    /**
+     * Check whether or not this inventory is empty. An inventory is considered
+     * to be empty if there are no ItemStacks in any slot of this inventory.
+     *
+     * @return true if empty, false otherwise
+     */
+    public boolean isEmpty();
+
     /**
      * Removes all stacks in the inventory matching the given material.
      *