fix: Avoid throwing exception when using NetworkList without a Networ…

…kManager [Up-port] (#3504)

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<!-- Add short version of the JIRA ticket to the PR title (e.g. "feat:
new shiny feature [MTT-123]") -->
Up-port of #3502  
Fixes #2539 


## Changelog

- Added: `LocalClientCannotWrite` function to co-locate the shared
functionality
- Fixed: Ensure that the `NetworkManager` exists before attempting to
access the `LocalClientId`

## Testing and Documentation

- No tests have been added.

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## Backport

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Backported in #3502

---------

Co-authored-by: unity-renovate[bot] <120015202+unity-renovate[bot]@users.noreply.github.com>
Co-authored-by: Emma <emma.mcmillan@unity3d.com>

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -10,6 +10,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Fixed `NullReferenceException` on `NetworkList` when used without a NetworkManager in scene. (#3503)
 - Fixed issue where `NetworkClient` could persist some settings if re-using the same `NetworkManager` instance. (#3491)
 - Fixed issue where a pooled `NetworkObject` was not resetting the internal latest parent property when despawned. (#3491)
 - Fixed issue where the initial client synchronization pre-serialization process was not excluding spawned `NetworkObject` instances that already had pending visibility for the client being synchronized. (#3488)

com.unity.netcode.gameobjects/Runtime/Messaging/Messages/NetworkVariableDeltaMessage.cs

@@ -144,9 +144,9 @@ public void Serialize(FastBufferWriter writer, int targetVersion)
                 var startingSize = writer.Length;
                 var networkVariable = NetworkBehaviour.NetworkVariableFields[i];
                 var shouldWrite = networkVariable.IsDirty() &&
-                    networkVariable.CanClientRead(TargetClientId) &&
-                    (networkManager.IsServer || networkVariable.CanClientWrite(networkManager.LocalClientId)) &&
-                    networkVariable.CanSend();
+                    networkVariable.CanClientRead(TargetClientId)
+                    && (networkManager.IsServer ||
+                    (networkVariable.CanWrite && networkVariable.CanSend()));
 
                 // Prevent the server from writing to the client that owns a given NetworkVariable
                 // Allowing the write would send an old value to the client and cause jitter

com.unity.netcode.gameobjects/Runtime/NetworkVariable/AnticipatedNetworkVariable.cs

@@ -217,7 +217,7 @@ public void Anticipate(T value)
             m_LastAnticipationCounter = m_NetworkBehaviour.NetworkManager.AnticipationSystem.AnticipationCounter;
             m_AnticipatedValue = value;
             NetworkVariableSerialization<T>.Duplicate(m_AnticipatedValue, ref m_PreviousAnticipatedValue);
-            if (CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            if (CanWrite)
             {
                 AuthoritativeValue = value;
             }

com.unity.netcode.gameobjects/Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -428,7 +428,7 @@ public IEnumerator<T> GetEnumerator()
         public void Add(T item)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkManager.LocalClientId))
+            if (CannotWrite)
             {
                 LogWritePermissionError();
                 return;
@@ -455,7 +455,7 @@ public void Add(T item)
         public void Clear()
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkManager.LocalClientId))
+            if (CannotWrite)
             {
                 LogWritePermissionError();
                 return;
@@ -493,7 +493,7 @@ public bool Contains(T item)
         public bool Remove(T item)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkManager.LocalClientId))
+            if (CannotWrite)
             {
                 LogWritePermissionError();
                 return false;
@@ -542,7 +542,7 @@ public int IndexOf(T item)
         public void Insert(int index, T item)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkManager.LocalClientId))
+            if (CannotWrite)
             {
                 LogWritePermissionError();
                 return;
@@ -578,7 +578,7 @@ public void Insert(int index, T item)
         public void RemoveAt(int index)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkManager.LocalClientId))
+            if (CannotWrite)
             {
                 throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
             }
@@ -610,7 +610,7 @@ public T this[int index]
             set
             {
                 // check write permissions
-                if (!CanClientWrite(m_NetworkManager.LocalClientId))
+                if (CannotWrite)
                 {
                     LogWritePermissionError();
                     return;

com.unity.netcode.gameobjects/Runtime/NetworkVariable/NetworkVariable.cs

@@ -128,7 +128,7 @@ public virtual T Value
             get => m_InternalValue;
             set
             {
-                if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
+                if (CannotWrite)
                 {
                     LogWritePermissionError();
                     return;
@@ -162,7 +162,7 @@ public bool CheckDirtyState(bool forceCheck = false)
             var isDirty = base.IsDirty();
 
             // A client without permissions invoking this method should only check to assure the current value is equal to the last known current value
-            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
+            if (CannotWrite)
             {
                 // If modifications are detected, then revert back to the last known current value
                 if (!NetworkVariableSerialization<T>.AreEqual(ref m_InternalValue, ref m_InternalOriginalValue))
@@ -245,7 +245,7 @@ public override bool IsDirty()
         {
             // If the client does not have write permissions but the internal value is determined to be locally modified and we are applying updates, then we should revert
             // to the original collection value prior to applying updates (primarily for collections).
-            if (!NetworkUpdaterCheck && m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId) && !NetworkVariableSerialization<T>.AreEqual(ref m_InternalValue, ref m_InternalOriginalValue))
+            if (!NetworkUpdaterCheck && CannotWrite && !NetworkVariableSerialization<T>.AreEqual(ref m_InternalValue, ref m_InternalOriginalValue))
             {
                 NetworkVariableSerialization<T>.Duplicate(m_InternalOriginalValue, ref m_InternalValue);
                 return true;
@@ -307,7 +307,7 @@ public override void ReadDelta(FastBufferReader reader, bool keepDirtyDelta)
         {
             // If the client does not have write permissions but the internal value is determined to be locally modified and we are applying updates, then we should revert
             // to the original collection value prior to applying updates (primarily for collections).
-            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId) && !NetworkVariableSerialization<T>.AreEqual(ref m_InternalOriginalValue, ref m_InternalValue))
+            if (CannotWrite && !NetworkVariableSerialization<T>.AreEqual(ref m_InternalOriginalValue, ref m_InternalValue))
             {
                 NetworkVariableSerialization<T>.Duplicate(m_InternalOriginalValue, ref m_InternalValue);
             }
@@ -349,7 +349,7 @@ public override void ReadField(FastBufferReader reader)
         {
             // If the client does not have write permissions but the internal value is determined to be locally modified and we are applying updates, then we should revert
             // to the original collection value prior to applying updates (primarily for collections).
-            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId) && !NetworkVariableSerialization<T>.AreEqual(ref m_InternalOriginalValue, ref m_InternalValue))
+            if (CannotWrite && !NetworkVariableSerialization<T>.AreEqual(ref m_InternalOriginalValue, ref m_InternalValue))
             {
                 NetworkVariableSerialization<T>.Duplicate(m_InternalOriginalValue, ref m_InternalValue);
             }

com.unity.netcode.gameobjects/Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -381,6 +381,16 @@ public bool CanClientWrite(ulong clientId)
             }
         }
 
+        /// <summary>
+        /// Returns true if the current <see cref="NetworkManager.LocalClientId"/> can write to this variable; otherwise false.
+        /// </summary>
+        internal bool CanWrite => m_NetworkManager && CanClientWrite(m_NetworkManager.LocalClientId);
+
+        /// <summary>
+        /// Returns false if the current <see cref="NetworkManager.LocalClientId"/> can write to this variable; otherwise true.
+        /// </summary>
+        internal bool CannotWrite => m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId);
+
         /// <summary>
         /// Returns the ClientId of the owning client
         /// </summary>