On collision with spawned enemy prefabs, my object gives NullReferenceException errors. Why is this happening ?

I have to note that my Object keeps getting activated and deactivated due to other connections/requirements in the game, which is normal. I’ve noticed that it is due to this activation and deactivation that the nullreferenceexception is thrown. Is there a way I can fix this ? I have the following OnTrigger2D detection code on my enemy prefabs:

void OnTriggerEnter2D(Collider2D blastCollisionCheck)
		if (blastCollisionCheck.gameObject.tag == "Radius") {

The error I receive is as follows, for the line - if (blastCollisionCheck.gameObject.tag == “Radius”) {

NullReferenceException: Object reference not set to an instance of an object
CrowdBehavior.OnTriggerEnter2D (UnityEngine.Collider2D blastCollisionCheck) (at Assets/Scripts/CrowdBehavior.cs:24)

This can happen if one collider collides with another collider, and the other one deletes the game object (or itself). When it comes time to call OnTriggerEnter, blastCollisionCheck is no longer valid. You should check blastCollisionCheck for null before using it. If it still fails, you probably will need to make it so that only one object allows the collision and destruction logically.