fix: Add null check in TrySetParent (#2625)

* fix: Add null check in TrySetParent

fixes #2621

* Added tests

* Changelog

---------

Co-authored-by: Noel Stephens <noel.stephens@unity3d.com>

Author: ShadauxCat

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -12,6 +12,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Fixed a crash when calling TrySetParent with a null Transform (#2625)
 - Fixed issue where a `NetworkTransform` using full precision state updates was losing transform state updates when interpolation was enabled. (#2624)
 - Fixed issue where `NetworkObject.SpawnWithObservers` was not being honored for late joining clients. (#2623)
 - Fixed issue where invoking `NetworkManager.Shutdown` multiple times, depending upon the timing, could cause an exception. (#2622)

com.unity.netcode.gameobjects/Runtime/Core/NetworkObject.cs

@@ -733,6 +733,12 @@ internal void SetNetworkParenting(ulong? latestParent, bool worldPositionStays)
         /// <returns>Whether or not reparenting was successful.</returns>
         public bool TrySetParent(Transform parent, bool worldPositionStays = true)
         {
+            // If we are removing ourself from a parent
+            if (parent == null)
+            {
+                return TrySetParent((NetworkObject)null, worldPositionStays);
+            }
+
             var networkObject = parent.GetComponent<NetworkObject>();
 
             // If the parent doesn't have a NetworkObjet then return false, otherwise continue trying to parent

testproject/Assets/Tests/Runtime/ObjectParenting/NetworkObjectParentingTests.cs

@@ -309,6 +309,49 @@ public IEnumerator SetParentTryAPI()
                 Assert.That(m_Cube_NetObjs[setIndex + 1].parent, Is.EqualTo(m_Dude_LeftArm_NetObjs[setIndex + 1]));
                 Assert.That(m_Cube_NetBhvs[setIndex + 1].ParentNetworkObject, Is.EqualTo(m_Dude_LeftArm_NetObjs[setIndex + 1].GetComponent<NetworkObject>()));
             }
+
+            Transform nullTransform = null;
+            GameObject nullGameObject = null;
+            NetworkObject nullNetworkObject = null;
+
+
+            Assert.That(m_Cube_NetObjs[0].GetComponent<NetworkObject>().TrySetParent(nullTransform));
+            Assert.That(m_Cube_NetBhvs[0].ParentNetworkObject, Is.EqualTo(null));
+
+            nextFrameNumber = Time.frameCount + 2;
+            yield return new WaitUntil(() => Time.frameCount >= nextFrameNumber);
+
+            for (int setIndex = 0; setIndex < k_ClientInstanceCount; setIndex++)
+            {
+                Assert.That(m_Cube_NetObjs[setIndex + 1].parent, Is.EqualTo(null));
+                Assert.That(m_Cube_NetBhvs[setIndex + 1].ParentNetworkObject, Is.EqualTo(null));
+            }
+
+
+            Assert.That(m_Cube_NetObjs[0].GetComponent<NetworkObject>().TrySetParent(nullGameObject));
+            Assert.That(m_Cube_NetBhvs[0].ParentNetworkObject, Is.EqualTo(null));
+
+            nextFrameNumber = Time.frameCount + 2;
+            yield return new WaitUntil(() => Time.frameCount >= nextFrameNumber);
+
+            for (int setIndex = 0; setIndex < k_ClientInstanceCount; setIndex++)
+            {
+                Assert.That(m_Cube_NetObjs[setIndex + 1].parent, Is.EqualTo(null));
+                Assert.That(m_Cube_NetBhvs[setIndex + 1].ParentNetworkObject, Is.EqualTo(null));
+            }
+
+
+            Assert.That(m_Cube_NetObjs[0].GetComponent<NetworkObject>().TrySetParent(nullNetworkObject));
+            Assert.That(m_Cube_NetBhvs[0].ParentNetworkObject, Is.EqualTo(null));
+
+            nextFrameNumber = Time.frameCount + 2;
+            yield return new WaitUntil(() => Time.frameCount >= nextFrameNumber);
+
+            for (int setIndex = 0; setIndex < k_ClientInstanceCount; setIndex++)
+            {
+                Assert.That(m_Cube_NetObjs[setIndex + 1].parent, Is.EqualTo(null));
+                Assert.That(m_Cube_NetBhvs[setIndex + 1].ParentNetworkObject, Is.EqualTo(null));
+            }
         }
     }
 }