coroutine issue

private IEnumerator changeTree(Vector2 vec) // Has to yield return something, even if you return null
    {
        print("IENUMERATOR STARTED!");
        Vector2 playerPos = (Vector2)player.transform.position;
        playerPos = new Vector2(Mathf.Round(playerPos.x), Mathf.Round(playerPos.y));
        while(playerPos - new Vector2(0,1) == vec || playerPos - new Vector2(0,2) == vec)
        {
            // Renderer renderer = GameObject.Find(vec.x + " , " + vec.y).GetComponent<Renderer>();
            // float alpha = GameObject.Find(vec.x + " , " + vec.y).GetComponent<Renderer>().material.color.a;
            GameObject prefab = GameObject.Find(vec.x + " , " + vec.y);

            // Dictionary<int, Transform> children = new Dictionary<int, Transform>();

            // int count = 0;

            foreach(Transform child in prefab.transform)
            {
                // children.Add(count, child);
                // count++;

                // child.GetComponent<SpriteRenderer>().color = new Color(0.1f, 0.1f, 0.1f);
                float alpha = child.GetComponent<SpriteRenderer>().color.a;

                if(alpha > 0.2f) child.GetComponent<SpriteRenderer>().color = new Color(1.0f, 1.0f, 1.0f, Mathf.Lerp(alpha, 0.2f, 2 * Time.deltaTime));
            }

            // float alpha = children[0].GetComponent<Renderer>().material.color.a;
            /*
            if(alpha > 0.2f)
            {
                // float newAlpha = Mathf.Lerp(alpha, 0.2f, 2 * Time.deltaTime);
                // children[0].GetComponent<Renderer>().material.color.a = newAlpha;
                // Renderer renderer = children[2].GetComponent<Renderer>();
                // renderer.material.color.a = Mathf.Lerp(alpha, 0.2f, 2 * Time.deltaTime);
                //children[2].alpha =
]           }*/
        }

        float alpha2 = 0.0f;
        while(alpha2 < 1.0f)
        {
            GameObject prefab = GameObject.Find(vec.x + " , " + vec.y);
            foreach(Transform child in prefab.transform)
            {
                alpha2 = child.GetComponent<SpriteRenderer>().color.a;

                child.GetComponent<SpriteRenderer>().color = new Color(1.0f, 1.0f, 1.0f, Mathf.Lerp(alpha2, 1.0f, 2 * Time.deltaTime));
            }
            // float alpha = GameObject.Find(vec.x + " , " + vec.y).GetComponent<Renderer>().material.color.a;
            // alpha =

            // if(alpha < 1.0f)
            // {
            //  alpha =
            // }
            // else yield return null;
        }

        tilesWithCoroutines.Remove(vec);
        print("COMPLETE!");
        yield return null;
    }