subclass_nil.rb

require 'fiddle'
require 'pry'

User = Struct.new :name

class NullUser < NilClass
  def self.new(*args, &block)
    obj           = Object.new
    obj_ptr       = Fiddle::Pointer.new 2*obj.object_id
    klass_ptr     = Fiddle::Pointer.new 2*self.object_id
    obj_ptr[8, 8] = klass_ptr.ref[0, 8]
    obj
  end

  def name
    ''
  end
end

user = User.new "Bob"  # => #<struct User name="Bob">
puts user.name                   # => "Bob"
puts user.to_h                   # => {:name=>"Bob"}
puts user = NullUser.new  # => nil
puts user.name            # => ""
puts user.to_h            # => {}

if user
  puts "User exists"
else
  puts "User aint real"
end
# => "User exists"
# But user _is nil_ lol