Fix double addition to sorted volume lists #1916

Author: FrancescoC-unity

com.unity.render-pipelines.core/Runtime/Volume/VolumeManager.cs

@@ -124,7 +124,8 @@ public void Register(Volume volume, int layer)
             // Look for existing cached layer masks and add it there if needed
             foreach (var kvp in m_SortedVolumes)
             {
-                if ((kvp.Key & (1 << layer)) != 0)
+                // We add the volume to sorted lists only if the layer match and if it doesn't contain the volume already.
+                if ((kvp.Key & (1 << layer)) != 0 && !kvp.Value.Contains(volume))
                     kvp.Value.Add(volume);
             }
 

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed an issue where even when set to OnDemand, the sky lighting would still be updated when changing sky parameters.
 - Fixed SSS materials appearing black in matcap mode.
 - Fixed rendering of custom passes in the Custom Pass Volume inspector
+- Fixed issue with volume manager trying to access a null volume.
 
 ### Changed
 - Remove MSAA debug mode when renderpipeline asset has no MSAA