pattern or rule i can't remember

Question

I read a long time ago about a rule that using an object we shouldn't point from one class to the other due to null possibility.

 class Foo
 {
   public Bar Bar1 {get; set;}

   public Foo()
   {

   }

 }

 class Bar
 {
     public string Name{ get; set;}
 }


 Foo foo = new Foo();
 foo.Bar1.Name;

what is the law or rule called after this pattern?

Answer 1

It's the Law of Demeter

To quote some of it:

In particular, an object should avoid invoking methods of a member object returned by another method. For many modern object oriented languages that use a dot as field identifier, the law can be stated simply as "use only one dot". That is, the code a.b().Method() breaks the law where a.Method() does not.

Answer 2

I think your referring to the Law of Demeter