@type t() :: %PolarExpress.Schemas.CustomerUpdatedMetadata{
  customer_email: String.t() | nil,
  customer_external_id: String.t() | nil,
  customer_id: String.t() | nil,
  customer_name: String.t() | nil,
  updated_fields: PolarExpress.Schemas.CustomerUpdatedFields.t() | nil
}