fix: NullReferenceException caused when unsubscribing on session removal [MTTB-1161] (#905)

* moving unsubscription to when session not null

* changelog addition

Author: fernando-cortez

Assets/Scripts/UnityServices/Sessions/MultiplayerServicesFacade.cs

@@ -78,7 +78,7 @@ public void BeginTracking()
             if (!m_IsTracking)
             {
                 m_IsTracking = true;
-                SubscribeToJoinedSessionAsync();
+                SubscribeToJoinedSession();
             }
         }
 
@@ -91,11 +91,11 @@ public void EndTracking()
             if (m_IsTracking)
             {
                 m_IsTracking = false;
-                UnsubscribeFromJoinedSessionAsync();
             }
 
             if (CurrentUnitySession != null)
             {
+                UnsubscribeFromJoinedSession();
                 if (m_LocalUser.IsHost)
                 {
                     DeleteSessionAsync();
@@ -232,7 +232,7 @@ void ResetSession()
             // no need to disconnect Netcode, it should already be handled by Netcode's callback to disconnect
         }
 
-        void SubscribeToJoinedSessionAsync()
+        void SubscribeToJoinedSession()
         {
             CurrentUnitySession.Changed += OnSessionChanged;
             CurrentUnitySession.StateChanged += OnSessionStateChanged;
@@ -244,7 +244,7 @@ void SubscribeToJoinedSessionAsync()
             CurrentUnitySession.SessionPropertiesChanged += OnSessionPropertiesChanged;
         }
 
-        void UnsubscribeFromJoinedSessionAsync()
+        void UnsubscribeFromJoinedSession()
         {
             CurrentUnitySession.Changed -= OnSessionChanged;
             CurrentUnitySession.StateChanged -= OnSessionStateChanged;

CHANGELOG.md

@@ -59,6 +59,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
   * Changed the way MeleeAction selects a target when there are multiple targets to collide with. The target with the highest GetTotalDamage value (mentioned above) will be selected.
 * Fixed a visual issue where a selected party member's party HUD slot would be displayed as selected (green) when the same or new party member joins the session in-game (#899)
 * Fixed Render Graph API compatibility mode warning and switched active input handling settings to "both" for removing InvalidOperationException (#901) 
+* Fixed error logged when unsubscribing from Session events when removed from a Session (#905)
 
 ## [2.5.0] - 2024-04-18