fix: Adds a null check for NetworkObjectReference => GameObject conversion [NCCBUG-172] (#2158)

* fix: Adds a null check for NetworkObjectReference => GameObject conversion [NCCBUG-172]

* Changelog

* style

* Update com.unity.netcode.gameobjects/Tests/Runtime/Serialization/NetworkObjectReferenceTests.cs

Co-authored-by: Jesse Olmer <jesseo@unity3d.com>

* Review feedback.

Co-authored-by: Jesse Olmer <jesseo@unity3d.com>

Author: ShadauxCat

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -13,6 +13,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 - Fixed ClientRpcs always reporting in the profiler view as going to all clients, even when limited to a subset of clients by ClientRpcParams. (#2144)
 - Fixed RPC codegen failing to choose the correct extension methods for FastBufferReader and FastBufferWriter when the parameters were a generic type (i.e., List<int>) and extensions for multiple instantiations of that type have been defined (i.e., List<int> and List<string>) (#2142)
+- Implicit conversion of NetworkObjectReference to GameObject will now return null instead of throwing an exception if the referenced object could not be found (i.e., was already despawned) (#2158)
 - Fixed throwing an exception in OnNetworkUpdate causing other OnNetworkUpdate calls to not be executed. (#1739)
 - Fixed warning resulting from a stray NetworkAnimator.meta file (#2153)
 

com.unity.netcode.gameobjects/Runtime/Serialization/NetworkObjectReference.cs

@@ -139,7 +139,16 @@ public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReade
         /// </summary>
         /// <param name="networkObjectRef">The <see cref="NetworkObjectReference"/> to convert from.</param>
         /// <returns>This returns the <see cref="GameObject"/> that the <see cref="NetworkObject"/> is attached to and is referenced by the <see cref="NetworkObjectReference"/> passed in as a parameter</returns>
-        public static implicit operator GameObject(NetworkObjectReference networkObjectRef) => Resolve(networkObjectRef).gameObject;
+        public static implicit operator GameObject(NetworkObjectReference networkObjectRef)
+        {
+            var networkObject = Resolve(networkObjectRef);
+            if (networkObject != null)
+            {
+                return networkObject.gameObject;
+            }
+
+            return null;
+        }
 
         /// <summary>
         /// Implicitly convert <see cref="GameObject"/> to <see cref="NetworkObject"/>.

com.unity.netcode.gameobjects/Tests/Runtime/Serialization/NetworkObjectReferenceTests.cs

@@ -110,6 +110,32 @@ public void TestSerializeGameObject()
             }
         }
 
+        [Test]
+        public void TestImplicitConversionToGameObject()
+        {
+            using var networkObjectContext = UnityObjectContext.CreateNetworkObject();
+            networkObjectContext.Object.Spawn();
+
+            NetworkObjectReference outReference = networkObjectContext.Object.gameObject;
+
+            GameObject go = outReference;
+            Assert.AreEqual(networkObjectContext.Object.gameObject, go);
+        }
+
+        [Test]
+        public void TestImplicitToGameObjectIsNullWhenNotFound()
+        {
+            using var networkObjectContext = UnityObjectContext.CreateNetworkObject();
+            networkObjectContext.Object.Spawn();
+
+            NetworkObjectReference outReference = networkObjectContext.Object.gameObject;
+
+            networkObjectContext.Object.Despawn();
+            Object.DestroyImmediate(networkObjectContext.Object.gameObject);
+
+            GameObject go = outReference;
+            Assert.IsNull(go);
+        }
         [Test]
         public void TestTryGet()
         {