test.rb

require "virtus"
require "rspec"
class Test
  include Virtus.model(:nullify_blank => true)
  attribute :name, String
end

RSpec.describe Test do
  it "should be nil" do
    test = Test.new(name: "")
    expect(test.name).to eq(nil)
  end
end

#Failures:

#  1) Test should be nil
#     Failure/Error: expect(test.name).to eq(nil)
#
#       expected: nil
#            got: ""
#
#       (compared using ==)
#     # ./test.rb:11:in `block (2 levels) in <top (required)>'