The defender isn't necessarily a player here

Besides, the defender doesn’t need to have the player data key anyways

src/main/java/com/gmail/nossr50/listeners/EntityListener.java

@@ -143,7 +143,7 @@ public class EntityListener implements Listener {
             return;
         }
 
-        if (!UserManager.hasPlayerDataKey(defender) || !defender.isValid() || !(defender instanceof LivingEntity)) {
+        if (Misc.isNPCEntity(defender) || !defender.isValid() || !(defender instanceof LivingEntity)) {
             return;
         }
 

src/main/java/com/gmail/nossr50/util/skills/CombatUtils.java

@@ -197,7 +197,7 @@ public final class CombatUtils {
         if (attacker instanceof Player && entityType == EntityType.PLAYER) {
             Player player = (Player) attacker;
 
-            if (Misc.isNPCEntity(player)) {
+            if (!UserManager.hasPlayerDataKey(player)) {
                 return;
             }