One approach is to execute Debug.Break() right at the same time you load your scene, then single-step the game one frame at a time. Remember scenes load the NEXT FRAME, not right now.
In general, some notes on how to fix a NullReferenceException error in Unity3D
- also known as: Unassigned Reference Exception
- also known as: Missing Reference Exception
The basic steps outlined above are:
- Identify what is null
- Identify why it is null
- Fix that.
Expect to see this error a LOT. It’s easily the most common thing to do when working. Learn how to fix it rapidly. It’s easy. See the above link for more tips.
This is the kind of mindset and thinking process you need to bring to this problem:
Step by step, break it down, find the problem.