Fix Sample installation in URP #122

Author: PaulDemeulenaere

com.unity.visualeffectgraph/CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fix [Case 1268354](https://fogbugz.unity3d.com/f/cases/1268354/)
 - Forbid creation of context in VisualEffectSubgraphBlock through edge dropping. No context should be allowed.
 - Fix [Case 1281861](https://issuetracker.unity3d.com/product/unity/issues/guid/1281861/)
+- Unexpected exception while installing samples inside an URP project [Case 1280065](https://issuetracker.unity3d.com/product/unity/issues/guid/1280065/)
 
 ## [8.2.0] - 2020-07-08
 

com.unity.visualeffectgraph/Editor/Models/Contexts/VFXSubgraphContext.cs

@@ -190,6 +190,7 @@ public void RecreateCopy()
             var graph = resource.GetOrCreateGraph();
             HashSet<ScriptableObject> dependencies = new HashSet<ScriptableObject>();
             graph.CollectDependencies(dependencies);
+            dependencies.RemoveWhere(o => o == null); //script is missing should be removed from the list before copy.
 
             var duplicated = VFXMemorySerializer.DuplicateObjects(dependencies.ToArray());
             m_SubChildren = duplicated.OfType<VFXModel>().Where(t => t is VFXContext || t is VFXOperator || t is VFXParameter).ToArray();