[Backport 8.x.x] Fixed a null ref exception in static sky when the default volume profile is invalid. (#302)

* Fixed a null ref exception in static sky when the default volume profile is invalid.

* Update changelog.

Author: JulienIgnace-Unity

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

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed the indirect diffuse texture not being ignored when it should (ray tracing disabled).
 - Fixed a performance issue with stochastic ray traced area shadows.
 - Made more explicit the warning about raytracing and asynchronous compute. Also fixed the condition in which it appears.
+- Fixed a null ref exception in static sky when the default volume profile is invalid.
 
 ### Changed
 - Shadowmask and realtime reflection probe property are hide in Quality settings

com.unity.render-pipelines.high-definition/Runtime/Sky/StaticLightingSky.cs

@@ -125,7 +125,9 @@ void UpdateCurrentStaticLightingSky()
                 var profileSkyParameters = m_SkySettingsFromProfile.parameters;
 
                 var defaultVolume = HDRenderPipeline.GetOrCreateDefaultVolume();
-                defaultVolume.sharedProfile.TryGet(skyType, out SkySettings defaultSky);
+                SkySettings defaultSky = null;
+                if (defaultVolume.sharedProfile != null) // This can happen with old projects.
+                    defaultVolume.sharedProfile.TryGet(skyType, out defaultSky);
                 var defaultSkyParameters = defaultSky != null ? defaultSky.parameters : null; // Can be null if the profile does not contain the component.
 
                 // Seems to inexplicably happen sometimes on domain reload.