Trying to reference a public property from another class/object and it's always null

I have a C# script attached to an empty object called GameManager. The script is GameManager.cs. Here are the first few lines:

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

public class GameManager : MonoBehaviour {
	public GameObject tilePrefab;
	public GameObject startTile;
	public GameObject lastTile;

I have another script attached to a camera called CameraManager.cs. I'm attempting to reference lastTile from GameManager but it's always null. Here is the full code for CameraManager.cs:

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

public class CameraManager : MonoBehaviour
{
	// Start is called before the first frame update
	private Vector3 currPos;
	private Vector3 newPos;
	public float CamMoveSpeed = 5f;
	GameManager gameManager;

	private void Awake() {
		gameManager = gameObject.AddComponent<GameManager>();
	}
	private void Start() {
	}

	private void Update() {
		if (gameManager.lastTile != null) {
			currPos = gameObject.transform.position;
			Vector3 tilePos = gameManager.lastTile.transform.position;
			newPos = new Vector3(currPos.x + tilePos.x, currPos.y + tilePos.y, currPos.z + tilePos.z);
			this.transform.position = Vector3.Lerp(currPos, newPos, CamMoveSpeed * Time.deltaTime);
			Debug.Log("Moving Camera...");
		} else {
			Debug.LogWarning("gameManager.lastTile is NULL");
		}
	}
}

This latest iteration is based on this SO question. The previous iteration was based on this SO question.

What is the proper way to reference a value from another script/class?

All I had to do was make the property public and then assign it in the inspector by dragging the GameManager object to the corresponding field. I was able to remove everything in the awake routine.

In the awake method of your camera class you assign gameManager with AddComponent, that will create a new instance of the GameManager script on the same object that your camera manager class is on, meaning that the reference that your camera manager class has to the GameManager class is not the one that’s on your GameManager gameObject.

What people do usually with GameManager classes is to use a Signlton structure

Basically you can have a static field of type GameManager in your GameManager class and assign it to its own instance on the Awake method of your GameManager class. Something like this

public class GameManager : MonoBehaviour {
    public GameObject tilePrefab = new GameObject("Name");
    public GameObject startTile = new GameObject("Name");
    public GameObject lastTile = new GameObject("Name");

    public static GameManager Instance;

    private void Awake(){
        Instance = this;
    }
}

And then you can use your game manager in any other class with this line GameManager.Instance.lastTitle

public class GameManager : MonoBehaviour {
    public GameObject tilePrefab;
    public GameObject startTile;
    public GameObject lastTile;
}

It doesnt look like your ever assigning these variables to anything, therefore they will always be null.

For them not to be null you need to assign them to something e.g.

public class GameManager : MonoBehaviour {
    public GameObject tilePrefab = new GameObject("Name");
    public GameObject startTile = new GameObject("Name");
    public GameObject lastTile = new GameObject("Name");
}

Or you can set them dynamically by doing

private void Update() {
    gameManager.lastTile = new GameObject("Name");
}