GUI script still shows GUI on different camera

private var enter : boolean;
var mySkin : GUISkin;

function OnGUI()
{
	GUI.skin = mySkin;
	if(enter)
	{
		GUI.Label(new Rect(Screen.width/2 - 75, Screen.height - 100, 200, 200), "TEXT");
	}
}

function OnTriggerEnter (other : Collider)
{
	if (other.gameObject.tag == "Player") 
	{
		enter = true;
	}
}

function OnTriggerExit (other : Collider)
{
	if (other.gameObject.tag == "Player") 
	{
		enter = false;
	}
}

So I have this script which works pretty well, however, whenever I turn off my first person controller and switch to a different camera the GUI still shows on screen? How would I get it to not show on a different camera?

Alright I managed to fix it by changing it to this:
private var enter : boolean;
var mySkin : GUISkin;

function OnGUI()
{
	GUI.skin = mySkin;
	if((enter) && (Camera.current.name == "Main Camera"))
	{
		GUI.Label(new Rect(Screen.width/2 - 75, Screen.height - 100, 200, 200), "TEXT");
	}
}

function OnTriggerEnter (other : Collider)
{
	if (other.gameObject.tag == "Player") 
	{
		enter = true;
	}
}

function OnTriggerExit (other : Collider)
{
	if (other.gameObject.tag == "Player") 
	{
		enter = false;
	}
}

However now I get a error message:
NullReferenceException: Object reference not set to an instance of an object
TV.OnGUI () (at Assets/Standard Assets/Character Controllers/Sources/Scripts/TV.js:7)