UnassignedReferenceException and Null-Check

Questions & Answers
1

I often check in Start()-method, if all needed references are set in inspector. So i wrote a utility method, for this like this:

public static void WarnIfNull(object o, string name) {
    if (o == null) {
        Debug.LogWarning(name + " is NULL");
...

so i can use it in component init code like this:

public class MyComponent : MonoBehavior {
    public AudioClip sound;
    void Start() {
        MyLogUtils.WarnIfNull(sound, "sound");
...

Nothing special, interesting so far… But it does not work. Assuming i forgot to assign reference in inspector. If i null-check inside of MyComponent.Start(), null check works correct. But if doing exact same null-check inside of MyLogUtils.WarnIfNull(), null check is FALSE. I can not explain this, it is really weird.

So i tryied to debug it, if object is not null, then what is it? (it was never assigned). I can cast it to AudioClip like this

if (o is AudioClip) {
    AudioClip a = (AudioClip) o; // this works
}

but if i call any method/property from this object like this:

var a_name = a.name;
a_name.ToString();

i am getting UnassignedReferenceException.

I know, it sounds strange, that null-check of same object in call-stack behaves not same. But is looks like this. I do not really understand what is the reason for that. Docs for UnassignedReferenceException somehow do not explain it.

So my missing-reference method looks like this now:

public static void WarnIfNull(object o, string name) {
    bool unassigned = false;
    if (o is AudioClip) {
        try {
            AudioClip a = (AudioClip) o;
            var a_name = a.name;
            a_name.ToString();
        } catch (UnassignedReferenceException e) {
            unassigned = true;
        }
    }
    if (o == null || unassigned) {
        Warn(name + " is NULL (unassigned in inspector, but somehow can be not null)");
    }
}

Any suggestions explanations are welcome. So, my question:

Why the same reference is null in one methode and not null in another. I just pass it by reference but, null-check result ist different. Is this some special UnityEditor stuff i should know?

2

So you don’t get any error when you use MyLogUtils.WarnIfNull(sound, “sound”); in Start()?

My guess would be that MyLogUtils isn’t there in your Start() method, maybe?

3

found answer: Custom == operator, should we keep it? | Unity Blog