what does it mean when it says "oh no, null."

Hola,

Breakdown! lol

Now let's temporarily add a public field that we will use to store the color of the GoKart. Let's make it the set to the String of "red".

Variable that is public. The variable stores the color of the GoKart. So the name makes sense to call GoKart. It's a string and the value is red.

So I have a public variable named GoKart that is = to red.

public class GoKart {
  public String mGoKart = "red";

}

Null - means that some value is null. Java can't have null values. If you get a Null, it's a null pointer exception. Meaning some variable being referenced does not have a value. It fails because you can't reference a variable without a value. What's the point? Well, for all intensive purposes 8 )

Let me know if that answers your question or if you have other issues I can help resolve.

Thanks!