Null-check entity UUID in WaypointCache (#6422)

* Add null check for entity UUID in WaypointCache

* Remove entity from uuid().toString()

* Remove parenthesis after uuid

Author: SleepyPopp

core/src/main/java/org/geysermc/geyser/session/cache/waypoint/WaypointCache.java

@@ -66,7 +66,12 @@ public void handlePacket(ClientboundTrackedWaypointPacket packet) {
     }
 
     public void addEntity(Entity entity) {
-        GeyserWaypoint waypoint = waypoints.get(entity.uuid().toString());
+        UUID uuid = entity.uuid();
+        if (uuid == null) {
+            return;
+        }
+
+        GeyserWaypoint waypoint = waypoints.get(uuid.toString());
         if (waypoint != null) {
             // On 1.26.0 and below:
             // This will remove the fake player packet previously sent to the client,
@@ -91,7 +96,12 @@ public void addEntity(Entity entity) {
     }
 
     public void removeEntity(Entity entity) {
-        GeyserWaypoint waypoint = waypoints.get(entity.uuid().toString());
+        UUID uuid = entity.uuid();
+        if (uuid == null) {
+            return;
+        }
+
+        GeyserWaypoint waypoint = waypoints.get(uuid.toString());
         if (waypoint != null) {
             // On 1.26.0 and below:
             // This will remove the player packet previously sent to the client,