hey, can i use a string variable (whichGemIGot) that is equal to a gameObjects name (Gem - Blue) ??? what i have now gets NullReferenceException

I know this is probably wrong i just cut out the bits that seemed needed to understand my situation. :P

var whichGemIGot : String;
function Update ()
{
    if(Input.GetButtonDown("Jump") && isShooter)
    {
        var child = transform.Find(whichGemIGot);
        child.rigidbody.AddRelativeForce(0,-1000,0);
        transform.DetachChildren();
        isShooter = false;
    }
}

function CreateGem ()
{
    var whichGem = Random.Range(1,7);
    switch(whichGem)
    {
        case 1:
            var Gem11 = Instantiate(Gem1, transform.position, transform.rotation);
            Gem11.parent = transform;
            whichGemIGot = "Gem - Blue";