MissingReferenceException: Error after destroying a moving game object - unity3d

Question

In my game some objects move every few seconds and others don't. I have created a the method below to handle the movement of moving objects.
private IEnumerator moveObject(GameObject movingObject, float posX, float duration) {
if(movingObject != null) {
float elapsedTime = 0;
Vector3 startPos = movingObject.transform.position;
Vector3 endpos = new Vector3(posX, objectPositionY, camera.nearClipPlane);//hole.transform.position;
while(movingObject != null && elapsedTime < duration) {
movingObject.transform.position = Vector3.Lerp(startPos, endpos, elapsedTime / duration);
elapsedTime += Time.deltaTime;
yield return null;
}
}
}
Also I destroy the moving objects using the code below:
for (int i = 0; i < holeObjects.Count; i++) {
Debug.Log ("countingholeobjectindex"+ i );
if (col.gameObject.Equals (holeObjects [i].getHoleObject ())) {
Debug.Log ("condition satisfied!" );
foreach( HoleObjectSetup holeItem in holeObjects )
{
if (holeItem.getHoleObjectType () == HoleObjectSetup.HoleObjectType.moving) {
int holeItemIndex = holeObjects.IndexOf(holeItem);
holeItem.StopAllCoroutines();
holeItem.DestroyHoleObject ();
//holeObjects.RemoveAll(item=>item==null);
//holeObjects.RemoveAt(holeItemIndex);
}
}
}
Any time I destroy a movingObject (mostly, when it's moving), I get the error
MissingReferenceException: The object of type 'GameObject' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
pointing to the line
movingObject.transform.position = Vector3.Lerp(startPos, endpos, elapsedTime / duration);
in the movingObject method (provided above). I tried adding another nullity check to surround the contents of the while loop, but that made Unity3d unresponsive, leaving me with the only option of force quitting. How can I resolve this issue?
UPDATE
movingObject is called in the coroutine below:
private IEnumerator MovementLogic(GameObject movingObject)
{
// keep going until deactivated or disabled
float currentPos = movingObject.transform.position.x;
while(filledPositions.Contains(currentPos))
{
float newPos = getNextPos(currentPos);
if(freePositions.Contains(newPos))
{
freePositions.Add (currentPos);
filledPositions.Remove (currentPos);
freePositions.Remove (newPos);
filledPositions.Add (newPos);
yield return moveObject(movingObject, newPos, movementDuration);
//update positions
yield return new WaitForSeconds(movementDelay);
currentPos = newPos;
}
else
{
// if a valid hole wasn't found, try the other direction next frame
ReverseDirection();
}
}
yield return null;
//}
}
UPDATE 2
The code for DestroyHoleObject() which is in HoleObjectSetup is:
public void DestroyHoleObject () {
Destroy (currentHoleObject);
}
and
public void createHoleObjectType (GameObject holeObject, HoleObjectType holeObjectType, Vector3 holeObjectPosition, bool isCollider2DEnabled) {
currentHoleObject = (GameObject)Instantiate (holeObject, holeObjectPosition, Quaternion.identity);
setHoleObjectType (holeObjectType);
}

Answer 1

Solve the problem by adding
Debug.Log
statements everywhere. It will take a few seconds to find out the exact point in the cycle that is causing problems.
Secondly,
Sometimes a cheap solution to these problems is, use
DestroyImmediate
rather than
Destroy
This might give you a quick fix.
Thirdly. Be more sophisticated about coroutines:
Something like ..
void OnEnable()
{
Debug.Log("enable ..");
}
void OnDisable()
{
StopCoroutine("Whatever");
.. or perhaps ..
StopAllCoroutines();
}
Moreover, ideally you should "handle it manually".
Consider the object you are getting rid of.
That class, should have a function something like this:
void BeingDestroyed()
{
.. carefully write your own code here to shut down the object ..
}
... and actually call that explicitly when you are about to destroy it.
It's not that easy to add, destroy stuff in games. It's often very complex.
Could be the object destroys itself: perform any needed shutdown code, wait a frame or two if that is relevant to you, remove from any lists, and then "destroy self".
You can't just "leave coroutines alone": you have to manage them carefully by hand.