reset all light estimation properties when unavailable

Assets/Scenes/LightEstimation/BasicLightEstimation.unity

   m_Name: 
   m_EditorClassIdentifier: 
   m_CameraManager: {fileID: 282840817}
-  m_Arrow: {fileID: 0}
 --- !u!114 &1015722069
 MonoBehaviour:
   m_ObjectHideFlags: 0

Assets/Scripts/BasicLightEstimation.cs

                 brightness = args.lightEstimation.averageBrightness.Value;
                 m_Light.intensity = brightness.Value;
             }
+            else
+            {
+                brightness = null;
+            }
 
             if (args.lightEstimation.averageColorTemperature.HasValue)
             {
+            else
+            {
+                colorTemperature = null;
+            }
+            }
+            else
+            {
+                colorCorrection = null;
             }
         }
 

Assets/Scripts/BasicLightEstimationUI.cs

         void SetUIValue<T>(T? displayValue, Text text) where T : struct
         {
             if (text != null)
-                text.text = displayValue.HasValue ? displayValue.Value.ToString(): k_UnavailableText;
+                text.text = displayValue.HasValue ? displayValue.Value.ToString(): "Unavailable";
-
-        const string k_UnavailableText = "Unavailable";
 
         BasicLightEstimation m_LightEstimation;
     }

Assets/Scripts/HDRLightEstimation.cs

             else
             {
                 arrow?.gameObject.SetActive(false);
+                mainLightDirection = null;
             }
 
             if (args.lightEstimation.mainLightColor.HasValue)
             }
+            else
+            {
+                mainLightColor = null;
+            }
 
             if (args.lightEstimation.mainLightIntensityLumens.HasValue)
             {
+            else
+            {
+                mainLightIntensityLumens = null;
+            }
 
             if (args.lightEstimation.ambientSphericalHarmonics.HasValue)
             {
+            }
+            else
+            {
+                sphericalHarmonics = null;
             }
         }