The class of the singleton object nil.
And—Returns false. obj is always evaluated as it is the argument to a method call—there is no short-circuit evaluation in this case.
Exclusive Or—If obj is nil or false, returns false; otherwise, returns true.
Always returns the string "nil".
call_seq:
nil.nil? => true
Only the object nil responds true to nil?.
Always returns an empty array.
nil.to_a #=> []
Always returns zero.
nil.to_f #=> 0.0
nil.to_i #=> 0
Always returns the empty string.
nil.to_s #=> ""
Or—Returns false if obj is nil or false; true otherwise.
[Validate]