Don't create a property manager if an entity has no properties

core/src/main/java/org/geysermc/geyser/entity/type/Entity.java

@@ -134,7 +134,7 @@ public class Entity implements GeyserEntity {
 
         this.valid = false;
 
-        this.propertyManager = new GeyserEntityPropertyManager(definition.registeredProperties());
+        this.propertyManager = definition.registeredProperties() == null ? null : new GeyserEntityPropertyManager(definition.registeredProperties());
 
         setPosition(position);
         setAirSupply(getMaxAir());
@@ -361,7 +361,7 @@ public class Entity implements GeyserEntity {
             return;
         }
 
-        if (propertyManager.hasProperties()) {
+        if (propertyManager != null && propertyManager.hasProperties()) {
             SetEntityDataPacket entityDataPacket = new SetEntityDataPacket();
             entityDataPacket.setRuntimeEntityId(geyserId);
             propertyManager.applyIntProperties(entityDataPacket.getProperties().getIntProperties());

core/src/main/java/org/geysermc/geyser/translator/protocol/java/JavaSelectKnownPacksTranslator.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2019-2024 GeyserMC. http://geysermc.org
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *
+ * @author GeyserMC
+ * @link https://github.com/GeyserMC/Geyser
+ */
+
+package org.geysermc.geyser.translator.protocol.java;
+
+import org.geysermc.geyser.network.GameProtocol;
+import org.geysermc.geyser.session.GeyserSession;
+import org.geysermc.geyser.translator.protocol.PacketTranslator;
+import org.geysermc.geyser.translator.protocol.Translator;
+import org.geysermc.mcprotocollib.protocol.data.game.KnownPack;
+import org.geysermc.mcprotocollib.protocol.packet.configuration.clientbound.ClientboundSelectKnownPacks;
+import org.geysermc.mcprotocollib.protocol.packet.configuration.serverbound.ServerboundSelectKnownPacks;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+
+@Translator(packet = ClientboundSelectKnownPacks.class)
+public class JavaSelectKnownPacksTranslator extends PacketTranslator<ClientboundSelectKnownPacks> {
+    // todo: dump from client?
+    private static final Set<String> KNOWN_PACK_IDS = Set.of("core", "update_1_21", "bundle", "trade_rebalance");
+
+    @Override
+    public void translate(GeyserSession session, ClientboundSelectKnownPacks packet) {
+        List<KnownPack> knownPacks = new ArrayList<>(1);
+        for (KnownPack pack : packet.getKnownPacks()) {
+            if ("minecraft".equals(pack.getNamespace()) && GameProtocol.getJavaMinecraftVersion().equals(pack.getVersion())) {
+                // Implementation note: these won't always necessarily be equal.
+                // 1.20.5 versus 1.20.6 for example - same protocol version. A vanilla server for either version will gracefully accept either.
+                // If the versions mismatch, the registry will be sent over the network, though.
+                // For vanilla compliancy, to minimize network traffic, and for potential future behavior,
+                // We'll implement how the Java client does it.
+                if (KNOWN_PACK_IDS.contains(pack.getId())) {
+                    knownPacks.add(pack);
+                }
+            }
+        }
+        session.sendDownstreamPacket(new ServerboundSelectKnownPacks(knownPacks));
+    }
+}