Fix failing nil test in about_nil

[#65851316]
Fix assert_equal method in about_nil

[#65851316]
Add undefined method string for expected match in about_nil

[#65851316]
Created equality fix in about_nil.rb as nil.nil is true

[#65851316]
Created equality fix as the string form of nil is an empty string; for about_nil.rb

[#65851316]
Created equality fix for about_nil.rb as nil.inspect is just the string nil

[#65851316]