Added null checks.

Assets/ScriptableRenderPipeline/HDRenderPipeline/HDRenderPipeline.cs

             Utilities.Destroy(m_DebugDisplayLatlong);
 
             m_SkyManager.Cleanup();
-            m_SsaoEffect.Cleanup();
+
+            if (m_SsaoEffect != null)
+                m_SsaoEffect.Cleanup();
 
 #if UNITY_EDITOR
             SupportedRenderingFeatures.active = SupportedRenderingFeatures.Default;

Assets/ScriptableRenderPipeline/HDRenderPipeline/ScreenSpace/AmbientOcclusion/AmbientOcclusion.cs

 
         public void Cleanup()
         {
-            m_Sheet.Release();
+            if (m_Sheet != null) m_Sheet.Release();
         }
     }
 }