NullReference is the single most common error while programming. Fixing it is always the same. - also known as: Unassigned Reference Exception - also known as: Missing Reference Exception - also known as: Object reference not set to an instance of an object Don't waste your life spinning around and round on this error. Instead, learn how to fix it fast... it's EASY!! Some notes on how to fix a NullReferenceException error in Unity3D: http://plbm.com/?p=221 The basic 3 steps outlined above are: 1. Identify what is null 2. Identify why it is null 3. 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. You need to figure out HOW that variable is supposed to get its initial value. There are many ways in Unity. In order of likelihood, it might be ONE of the following: - drag it in using the inspector - code inside this script initializes it - some OTHER external code initializes it - ? something else? This is the kind of mindset and thinking process you need to bring to this problem: https://forum.unity.com/threads/why-do-my-music-ignore-the-sliders.993849/#post-6453695 Step by step, break it down, find the problem. Here is an analogy of a null reference: - I give you an empty cookie jar - I tell you to take a cookie from the jar Your job is to identify which jar is empty, find out why it is empty, and fix that.