Background

I am trying to create an embedded schema that needs to save information about orders.
Sometimes orders have no customer_id and that is fine (for the application).

defmodule Order do
  use Ecto.Schema

  embedded_schema do
    field(:customer_id, :integer | nil)
    field(:stage, enum: [:bought | :in_shop_cart | :canceled])
    field(:details, :string)
  end
end

Problem

The issue here is that I get a compile error for customer_id:

(CompileError) misplaced operator |/2

The | operator is typically used between brackets as the cons operator:

    [head | tail]

where head is a single element and the tail is the remaining of a list.
It is also used to update maps and structs, via the %{map | key: value} notation,
and in typespecs, such as @type and @spec, to express the union of two types

I understand the issue here is the use of :integer | nil. This is not a list, so the advice I get is not usable.

Question

How can I represent optional values in my embedded schema ? (specifically :something | nil)