fix: avoid throwing exception when using NetworkList without a NetworkManager (#2539)

Author: PitouGames

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -17,6 +17,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 - Fixed issue where `NetworkVariable`s on a `NetworkBehaviour` could fail to synchronize changes if one has `NetworkVariableUpdateTraits` set and is dirty but is not ready to send. (#3465)
 - Fixed issue where when a client changes ownership via RPC the `NetworkBehaviour.OnOwnershipChanged` can result in identical previous and current owner identifiers. (#3434)
+- Fixed `NullReferenceException` on `NetworkList` when used without a NetworkManager in scene. (#2539)
 
 ### Changed
 

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

@@ -425,7 +425,7 @@ public IEnumerator<T> GetEnumerator()
         public void Add(T item)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
             {
                 LogWritePermissionError();
                 return;
@@ -452,7 +452,7 @@ public void Add(T item)
         public void Clear()
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
             {
                 LogWritePermissionError();
                 return;
@@ -490,7 +490,7 @@ public bool Contains(T item)
         public bool Remove(T item)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
             {
                 LogWritePermissionError();
                 return false;
@@ -539,7 +539,7 @@ public int IndexOf(T item)
         public void Insert(int index, T item)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
             {
                 LogWritePermissionError();
                 return;
@@ -575,7 +575,7 @@ public void Insert(int index, T item)
         public void RemoveAt(int index)
         {
             // check write permissions
-            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
             {
                 LogWritePermissionError();
                 return;
@@ -608,7 +608,7 @@ public T this[int index]
             set
             {
                 // check write permissions
-                if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+                if (m_NetworkManager && !CanClientWrite(m_NetworkManager.LocalClientId))
                 {
                     LogWritePermissionError();
                     return;