null reference on this code

im getting a null reference on this code and i can’t figure out why… if you can help it would be much appreciated… i wont post the whole script as my game scripts are large and vastly confusing :L

       if(Targets.Count >= 1)
        {
            if (gameObject.GetComponent<Mob>().IsZombie == true)
            {
                List<Transform> transtemp = new List<Transform>();

                foreach (Transform zombie in Targets)
                {
                    if (zombie.gameObject.GetComponent<Mob>().IsZombie == true)
                    {
                        transtemp.Add(zombie);
                    }                 
                }

                foreach (Transform zombie in transtemp)
                {
                    Targets.Remove(zombie);
                }
            }

plz post the full error message stack which you are getting as well