TextMesh Pro Change text in script NullReferenceException

I'm making a VR scene and trying to display the time left in game in a TextMesh Pro. I'm updating the time in a script, with a public TextMeshPro variable so I can pass the object there, but it throws a NullReferenceException.

Hirarchy : (parent) emptyObject with script attached -> (child) Text - TextMeshPro

Script code:
public TextMeshPro timeText;
...
void Update()
{
if(timeLeft >= 0){
timeLeft -= Time.deltaTime;
timeText.text = "Time: " + ((int)timeLeft).ToString (); }

The weird thing is that the text gets updated on the screen, but it still throws a NullReferenceException on the last line of the Update() function and says that timeText is null. Any idea what's happening here?