NullReferenceException: Reference types

Now we understand stack traces, we know what line is throwing the NullReferenceException.

On this line, only reference types can be null:

class, interface, and delegate types are reference types. struct is not.

Usually, this can be reduced to complex, and simple types:

Complex types tend to be reference types, such as Component, GameObject, or List.
Simple structures tend to be structs, such as int, float, Vector3, or Quaternion.

You can double-check types by using IDE inspection, or via the documentation.

You can see a more detailed breakdown of value and reference types here.

Unity, huh, how?