SPIGOT-5805: NPE when getting an Attribute from a Player

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/attribute/Attribute.java

@@ -1,6 +1,5 @@
 package org.bukkit.attribute;
 
-import java.util.Locale;
 import org.bukkit.Keyed;
 import org.bukkit.NamespacedKey;
 import org.jetbrains.annotations.NotNull;
@@ -13,56 +12,60 @@ public enum Attribute implements Keyed {
     /**
      * Maximum health of an Entity.
      */
-    GENERIC_MAX_HEALTH,
+    GENERIC_MAX_HEALTH("generic.max_health"),
     /**
      * Range at which an Entity will follow others.
      */
-    GENERIC_FOLLOW_RANGE,
+    GENERIC_FOLLOW_RANGE("generic.follow_range"),
     /**
      * Resistance of an Entity to knockback.
      */
-    GENERIC_KNOCKBACK_RESISTANCE,
+    GENERIC_KNOCKBACK_RESISTANCE("generic.knockback_resistance"),
     /**
      * Movement speed of an Entity.
      */
-    GENERIC_MOVEMENT_SPEED,
+    GENERIC_MOVEMENT_SPEED("generic.movement_speed"),
     /**
      * Flying speed of an Entity.
      */
-    GENERIC_FLYING_SPEED,
+    GENERIC_FLYING_SPEED("generic.flying_speed"),
     /**
      * Attack damage of an Entity.
      */
-    GENERIC_ATTACK_DAMAGE,
+    GENERIC_ATTACK_DAMAGE("generic.attack_damage"),
+    /**
+     * Attack knockback of an Entity.
+     */
+    GENERIC_ATTACK_KNOCKBACK("generic.attack_knockback"),
     /**
      * Attack speed of an Entity.
      */
-    GENERIC_ATTACK_SPEED,
+    GENERIC_ATTACK_SPEED("generic.attack_speed"),
     /**
      * Armor bonus of an Entity.
      */
-    GENERIC_ARMOR,
+    GENERIC_ARMOR("generic.armor"),
     /**
      * Armor durability bonus of an Entity.
      */
-    GENERIC_ARMOR_TOUGHNESS,
+    GENERIC_ARMOR_TOUGHNESS("generic.armor_toughness"),
     /**
      * Luck bonus of an Entity.
      */
-    GENERIC_LUCK,
+    GENERIC_LUCK("generic.luck"),
     /**
      * Strength with which a horse will jump.
      */
-    HORSE_JUMP_STRENGTH,
+    HORSE_JUMP_STRENGTH("horse.jump_strength"),
     /**
      * Chance of a zombie to spawn reinforcements.
      */
-    ZOMBIE_SPAWN_REINFORCEMENTS;
+    ZOMBIE_SPAWN_REINFORCEMENTS("zombie.spawn_reinforcements");
 
     private final NamespacedKey key;
 
-    private Attribute() {
+    private Attribute(String key) {
-        this.key = NamespacedKey.minecraft(this.name().toLowerCase(Locale.ROOT));
+        this.key = NamespacedKey.minecraft(key);
     }
 
     @NotNull