Merge pull request #1376 from stride3d/dev/tebjan/fix-for-pr-1346

[Rendering] Fixes null exception on first frame. #1343

sources/engine/Stride.Engine/Rendering/ModelRenderProcessor.cs

@@ -125,7 +125,7 @@ namespace Stride.Rendering
                 isShadowCaster &= modelMaterialInstance.IsShadowCaster;
 
             if (isShadowCaster != renderMesh.IsShadowCaster
-                || materialPass.HasTransparency != renderMesh.MaterialPass.HasTransparency)
+                || materialPass.HasTransparency != renderMesh.MaterialPass?.HasTransparency)
             {
                 renderMesh.IsShadowCaster = isShadowCaster;
                 VisibilityGroup.NeedActiveRenderStageReevaluation = true;