Passed a test in about_nil.rb

Unlike NULL in other languages, nil is its own object that methods can be called on.

[#54146055]
Passed a test in about_nil.rb

Calling a method that the nil object doesn't have returns a NoMethodError, not a null pointer exception.

[#54146055]
Passed a test in about_nil.rb

Nil does have methods defined on it that can be called freely, including a method from Object that checks if something is nil.

(It's probably better to use obj.nil? because the == operator can be easily redefined for obj.)

[#54146055]
Merge pull request #3 from ArGroves/54146055_about_nil_master

about nil master

[Delivers #54146055]