Trouble with Null Reference in Script

Questions & Answers
1

Hello everyone, I’m having a hard time tracking down a null reference error that is occuring between 2 scripts. Just so you know, sometimes the script will fail early (on the 2nd time it activates) or will fail late (after 10+ activations).

For your reference, here is the full error:
NullReferenceException: Object reference not set to an instance of an object
PushPlatform.Push () (at Assets/Scripts/Rooms/Room 12/PushPlatform.cs:20)
PushPlatformManager+c__Iterator3.MoveNext () (at Assets/Scripts/Rooms/Room 12/PushPlatformManager.cs:52)

Here is the 1st script that the error references, the error occurs at: “if (hit.rigidbody.tag == “TDPlatform”)”

using UnityEngine;
using System.Collections;

public class PushPlatform : MonoBehaviour {
	public float pushPower; //100?, 

	void FixedUpdate () 
	{
		//Push();
	}
	
	public void Push ()
	{
		//if (Input.GetKey (KeyCode.P))
		//{
		//Debug.Log ("P");
		RaycastHit hit;
		Physics.Raycast(transform.position, -transform.up, out hit, 10f);
			Debug.DrawRay(transform.position,-transform.up, Color.red);
			if (hit.rigidbody.tag == "TDPlatform")
			{
				hit.rigidbody.AddForceAtPosition (-transform.up * pushPower, hit.point, ForceMode.Impulse);
				Debug.Log ("Pusher hit " + hit.rigidbody.name);
			}

			else
			{
				Debug.Log ("the pusher hit something besides the platform");
			}
		//}
	}
}

And here is the 2nd script it references, the error will change but it occurs on one of the case lines ( pushPlatformArray [0,1,2].Push();).

using UnityEngine;
using System.Collections;

public class PushPlatformManager : MonoBehaviour {
	// this script goes on TDPlatform1stPlayerLayer, 
	public float waitBetweenFire; //xx, 
	public int randomNumber;
	public PushPlatform[] pushPlatformArray;
	public bool selectionInProgress;


	void Awake ()
	{
		selectionInProgress = false;
		pushPlatformArray = new PushPlatform[4];
		pushPlatformArray = gameObject.GetComponentsInChildren <PushPlatform>();
	}




	void FixedUpdate ()
	{
		Fire();
	}


	void Fire()
	{
		if (selectionInProgress == false)
		{
		StartCoroutine (TriggerPusher(waitBetweenFire));
		}
	}


	IEnumerator TriggerPusher (float time)
	{
		selectionInProgress = true;
		Debug.Log ("selectionInProgress is " + selectionInProgress);
		yield return new WaitForSeconds (time);
		randomNumber = Random.Range (0,3);

		switch (randomNumber)
		{
			case 0: 
			pushPlatformArray [0].Push();
			Debug.Log ("pushPlatformArray [0] should have pushed");
			break;

			case 1: 
			pushPlatformArray [1].Push();
			Debug.Log ("pushPlatformArray [1] should have pushed");
			break;

			case 2: 
			pushPlatformArray [2].Push();
			Debug.Log ("pushPlatformArray [2] should have pushed");
			break;

			case 3: 
			pushPlatformArray [3].Push();
			Debug.Log ("pushPlatformArray [3] should have pushed");
			break;

			default:
			Debug.Log ("ranndom number failed to trigger a push");
			break;
		}
		selectionInProgress = false;
		Debug.Log ("selectionInProgress is " + selectionInProgress);
	}
}
2

The problem is, that the raycast is not hitting anything or at least nothing with a rigidbody. The raycast function is of type boolean, so you can check, if it hits anything.
If it hit anything, you should check, if the hit object has a rigidbody, you can simply check this with if(hit.rigidbody). Try the following:

if(Physics.Raycast(transform.position, -transform.up, out hit, 10f)){
  if(hit.rigidbody){
    if (hit.rigidbody.tag == "TDPlatform")
    {
      hit.rigidbody.AddForceAtPosition (-transform.up * pushPower, hit.point, ForceMode.Impulse);
      Debug.Log ("Pusher hit " + hit.rigidbody.name);
    }
    else
    {
      Debug.Log ("the pusher hit something besides the platform");
    }
  }else{
    //Here the hit object does not have a rigidbody
  }
}else{
  //Here the raycast did not hit anything
}
3

hit.rigidbody.tag

should be

hit.transform.tag