ActiveModel::Attribute generates non nilable attribute that should be nilable

I have the following class (whole content):

# app/models/vacancy.rb

# typed: true
# frozen_string_literal: true

class Vacancy < ApplicationRecord
  attribute :startlatest, :datetime
end

I generates the DSL to have a non nilable startlatest:

# sorbet/rbi/dsl/vacancy.rbi

class Vacancy
  include GeneratedAttributeMethods
  # [...]

  private

  module GeneratedAttributeMethods
    # [...]

    sig { returns(::ActiveSupport::TimeWithZone) }
    def startlatest; end

    sig { params(value: ::ActiveSupport::TimeWithZone).returns(::ActiveSupport::TimeWithZone) }
    def startlatest=(value); end

    # [...]
  end
end

Why does it assume the attribute is not nilable in this case? Shouldn't it be nilable?

Tapioca v0.16.11

Start with the reproduction in app/models/vacancy.rb and compare it with the generated sorbet/rbi/dsl/vacancy.rbi output. Trace how the attribute DSL determines the getter and setter types, then verify that a datetime attribute without a value produces nullable signatures in the generated RBI.