Instantiate a class type from inside a variable?

Hi, I have a few Boss AI classes that inherit from the class Boss. In inspector, I can drag in a BossAI script as an object (BossClass), but I'm not able to properly instantiate it. ![alt text][1] this compiles but throws this error: "NullReferenceException: Object reference not set to an instance of an object" [1]: /storage/temp/197344-f20cbf0fd21410ccce7d5d7da15ce6e0.png