NullReferenceException when using messaging system

Hello everyone, I decided to implement a simple messaging system into my project. I'm using this one: CSharpMessenger Extended (it's implemented with static methods).

It's very strange that when I call a method directly everything is working correctly. But when I broadcast a message with the messaging system I get a NullReferenceException on some of the game objects. To my surprise adding the line if (_gameObject == null) return; solves the problem. However it's not an option to add a check if the object is null to every place where I get this exception.

What might be the problem?

Here's my code for broadcasting a message:

 public class Head : MonoBehaviour {
 
     public Snake snake;
     
     void OnControllerColliderHit (ControllerColliderHit hit)
     {
         if ( hit.gameObject.GetComponent<Terrain>() )
             return;
 
             //This way everything was working without any surprises.
             //snake.PropCollected( hit.gameObject.GetComponent<Prop>() );
             //Using messaging system instead
         if ( hit.gameObject.GetComponent<Prop>() )
             Messenger<Prop>.Broadcast( "prop collected", hit.gameObject.GetComponent<Prop>() );
             Destroy(hit.gameObject);
 
         }
     }

Here's how I subscribe to the event and respond to it:

 public class Snake : MonoBehaviour {
     
     public GameObject headBlock;
 
     public GameObject snakeBlocks;
 
     int lastSnakeBlockId;
 
     private GameObject FindBlockWithId( int _id )
     {
             if (!snakeBlocks) return null;    //This line somehow solves the problem; However the object is 100% assigned in the editor.
     
             foreach (Transform child in snakeBlocks.transform) {
                  if (child.gameObject.GetComponent<SnakeBlockScript>().blockId == _id)
                  {
                      return child.gameObject;
                  }
             }
 
         return headBlock;
     }
     
     void Awake()
     {
         //Set up message listeners
         Messenger<Prop>.AddListener("prop collected", AddBlock);    
     }
 
     public void AddBlock(Prop _prop)
     {
         GameObject lastBlock = FindBlockWithId(lastSnakeBlockId - 1);
         if (!lastBlock) return;
 
         //Some more code
         //...
     }
 }

Thank you!