NullReferenceException error when assigning a list to new()

[Kurt-Dekker]

The answer is always the same… ALWAYS!

How to fix a NullReferenceException error

https://forum.unity.com/threads/how-to-fix-a-nullreferenceexception-error.1230297/

Three steps to success:

• Identify what is null ← any other action taken before this step is WASTED TIME
• Identify why it is null
• Fix that

Generally, DO NOT make fields public if you’re going to be modifying them in code. Unity WILL modify these fields as part of any normal serialization. Either make them public to drag stuff in and leave it alone, or make them private and provide an API to manipulate their contents. Here’s why:

Serialized / public fields in Unity are initialized as a cascade of possible values, each subsequent value (if present) overwriting the previous value:

• what the class constructor makes (either default(T) or else field initializers, eg “what’s in your code”)

• what may be saved with the prefab

• what may be saved with the prefab override(s)/variant(s)

• what may be saved in the scene and not applied to the prefab

• what may be changed in the scene and not yet saved to disk

• what may be changed in OnEnable(), Awake(), Start(), or even later

Make sure you only initialize things at ONE of the above levels, or if necessary, at levels that you specifically understand in your use case. Otherwise errors will seem very mysterious.

Here’s the official discussion: Serialization in Unity

If you must initialize fields, then do so in the void Reset() method, which ONLY runs in the UnityEditor.

Field initializers versus using Reset() function and Unity serialization:

Sensitivity in my MouseLook script.

Whatever value you set and save in your scene or prefab will wipe out the field initializer value you change in the code above. This is a common source of confusion: the object is created, so at that instant in time it has the value you set in code, but before the object is put into use, if Unity has a saved scene or saved prefab that this is already in, then the value saved is overwritten. It’s best to remove the initialization value above and instead provide it in a Reset function: public f…

Crouch speed is faster than Movement Speed

If something is public: The instant you add that to your scene / prefab it is 10f … AND THEN IT GETS SERIALIZED. Now go change the value in code. Note that it has no effect: the serialized value writes over the code value. This is how Unity serialization works. If you want to define it in code, make the variable private. If you want to define it in the editor, make it public and DO NOT INITIALIZE IT. Instead, make a Reset function, which ONLY runs at the instant it is added: void Reset(…

To avoid complexity in your prefabs / scenes, I recommend NEVER using the FormerlySerializedAsAttribute