added null check for scenario before adding tag

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerTag.cs

     [Serializable]
     public abstract class RandomizerTag : MonoBehaviour
     {
+        ScenarioBase scenario => ScenarioBase.activeScenario;
+
-            ScenarioBase.activeScenario.tagManager.AddTag(GetType(), gameObject);
+            if (scenario)
+                scenario.tagManager.AddTag(GetType(), gameObject);
-            var scenario = ScenarioBase.activeScenario;
             if (scenario)
                 scenario.tagManager.RemoveTag(GetType(), gameObject);
         }