问题理解Ruby错误：nil的未定义方法`<<'：NilClass（NoMethodError）

I'm fairly new to Ruby and have tried to research this problem. Here is the code so far. I don't seem to have this problem calling the user object (user.deal_one(mydeck.deal_card)), but when I call it on the dealer I get this same error. The dealer object has the same instance variables and am unsure why it is calling on the method '<<'. I'm fairly new to Ruby and have tried to resear