Fixed all tests in about_nil.rb

- Learned that nil is an object.
- Learned that calling a method that nil doesn't know about
  would return NoMethodError with "undefined method" message.
  Learned that nil has several methods: #nil?, #to_s, #inspect.

[#65851740]
Merge pull request #2 from mkreyman/65851740_about_nil_master

Fixed all tests in about_nil.rb

[Delivers #65851740]