NullReferenceException — practical investigation

NullReferenceException

NullReferenceException tells you that code tried to use a reference that was null. It does not by itself prove which object was null or why.

Useful investigation order

1. Find the first relevant NullReferenceException and nearby stack/context lines.
2. Identify the first frame or method that belongs to your mod or the exact vanilla component you touched.
3. Ask whether the object was expected to exist at that lifecycle moment.
4. If this followed UI cloning, inspect copied MonoBehaviour / EventTrigger components before adding broad null checks.
5. Reproduce with the smallest path possible and log the objects/fields immediately before the failing call.

UI warning

TerraForge reproduced a NullReferenceException by cloning an active vanilla UI cell whose copied behavior executed Awake() in the wrong context. The fix was not “add a null check everywhere”; it was to change the cloning lifecycle and remove unsafe copied behavior.

See Clone vanilla UI more safely.