how to initiate animation from implementing script in state machine?

Hello all,

I've been implementing my own state machine C# scripts based on this tutorial by @MatthewSchell, which is a very good one btw . There's a thing I can't understand. Say I get a function PatrolState() , which is being called from the MonoBehaviour script StatePatternEnemy. and while in PatrolState I want my enemy to become Idle (as it's part of the animatorController animations attached to the enemy). So I've set a "public Animator animator" on the StatePatternEnemy, and expected that when calling Idle from PatrolState, by: animator.SetBool("Idle", true) - it'll work. Instead it gives me a nullReference error. (Object reference not set to an instance of an object).

What am I doing wrong? perhaps I'm not understanding the relationships between the scripts.

Thank you!