got an error Object reference not set to an instance of an object

I am a newbie and I'm working through a tutorial called survival shooter. I'm using V5.4.2. I downloaded the updated assets and I'm working on the 7th lesson. When I run the game, using unity's script, I am getting an error (actually 2) both refer to NullREferenceException : Object not set to an instance of an object. I checked the script and on line 26 of the EnemyMovement script and line 65 on the EnemyAttack It seems ok (for all I know), so I was wondering where best to look . One is EnemyMovement.Update() and the other is EnemyAttack.Update(). It might be one mistake that shows up or affects two items. Need a bit of expertise. Thanks.