Getting an Exception on Endless Runner 3D game

Questions & Answers
1

I referred to the tutorial series of: [Catlike Coding][1]

Situation: I am trying to implement Endless runner 3D game by referring the above tutorial.
What happened is that when i implemented PlatformManager script, it says

InvalidOperationException: Operation
is not valid due to the current state
of the object
System.Collections.Generic.Queue`1[UnityEngine.Transform].Peek
() PlatformManager.Update () (at
Assets/Platform/PlatformManager.cs:35)

There is a simple object pooling going on here,I searched google for days and couldn’t find the answer.
here is the PlatformManager.cs script:

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class PlatformManager  : MonoBehaviour {
	public Transform prefab;
	public int numberOfObjects;
	public float recycleOffset;
	public Vector3 startPosition;
    public Vector3 minSize, maxSize,minGap, maxGap;
	public float minY, maxY;
	private Vector3 nextPosition;
	private Queue<Transform> objectQueue;

	void Start () {
		objectQueue = new Queue<Transform>(numberOfObjects);
		for (int i = 0; i < numberOfObjects; i++) {
			objectQueue.Enqueue((Transform)Instantiate(prefab));
		}
		nextPosition = startPosition;
		for (int i = 0; i < numberOfObjects; i++) {
			Transform o = (Transform)Instantiate(prefab);
			o.localPosition = nextPosition;
			nextPosition.x += o.localScale.x;
			objectQueue.Enqueue(o);
		}
	}
	void Update () {
		if (objectQueue.Peek().localPosition.x + recycleOffset < Runner.distanceTraveled) {
			Transform o = objectQueue.Dequeue();
			o.localPosition = nextPosition;
			nextPosition.x += o.localScale.x;
			objectQueue.Enqueue(o);
			Recycle();
		}
	}
	private void Recycle () {
	Vector3 scale = new Vector3(
			Random.Range(minSize.x, maxSize.x),
			Random.Range(minSize.y, maxSize.y),
			Random.Range(minSize.z, maxSize.z));
		Vector3 position = nextPosition;
		position.x += scale.x * 0.5f;
		position.y += scale.y * 0.5f;
		Transform o = objectQueue.Dequeue();
		o.localScale = scale;
		o.localPosition = position;
		nextPosition.x += scale.x;
		objectQueue.Enqueue(o);
		
		nextPosition += new Vector3(
			Random.Range(minGap.x, maxGap.x) + scale.x,
			Random.Range(minGap.y, maxGap.y),
			Random.Range(minGap.z, maxGap.z));

		if(nextPosition.y < minY){
			nextPosition.y = minY + maxGap.y;
		}
		else if(nextPosition.y > maxY){
			nextPosition.y = maxY - maxGap.y;
		}
	}
}

How can i get rid of this error?
Thanks in advance.
[1]: Runner, a Unity C# Tutorial

2

Haven’t read the whole code but that exception comes when the Queue is empty. Peek method reads the top element of the stack and when it is null it gives that exception.