Allow barcode to be nullable (really this time)

See OAI/OpenAPI-Specification#1368 for why the earlier approach was unsuccessful

lib/cocina/models/identification.rb

@@ -4,7 +4,7 @@ module Cocina
   module Models
     class Identification < Struct
       # A barcode
-      attribute :barcode, Types::Nominal::Any.optional.meta(omittable: true)
+      attribute :barcode, Types::Nominal::Any.meta(omittable: true)
       attribute :catalogLinks, Types::Strict::Array.of(CatalogLink).default([].freeze)
       # Digital Object Identifier (https://www.doi.org)
       # example: 10.25740/bc123df4567

lib/cocina/models/request_identification.rb

@@ -4,7 +4,7 @@ module Cocina
   module Models
     class RequestIdentification < Struct
       # A barcode
-      attribute :barcode, Types::Nominal::Any.optional.meta(omittable: true)
+      attribute :barcode, Types::Nominal::Any.meta(omittable: true)
       attribute :catalogLinks, Types::Strict::Array.of(CatalogLink).default([].freeze)
       # Unique identifier in some other system. This is because a large proportion of what is deposited in SDR, historically and currently, are representations of objects that are also represented in other systems. For example, digitized paper and A/V collections have physical manifestations, and those physical objects are managed in systems that have their own identifiers. Similarly, books have barcodes, archival materials have collection numbers and physical locations, etc. The sourceId allows determining if an item has been deposited before and where to look for the original item if you're looking at its SDR representation. The format is: "namespace:identifier"
 

openapi.yml

@@ -314,7 +314,6 @@ components:
             $ref: "#/components/schemas/DescriptiveBasicValue"
     Barcode:
       description: 'A barcode'
-      nullable: true
       oneOf:
         - $ref: '#/components/schemas/BusinessBarcode'
         - $ref: '#/components/schemas/LaneMedicalBarcode'
@@ -1845,6 +1844,7 @@ components:
     StandardBarcode:
       description: The standard barcode associated with a DRO object, prefixed with 36105
       type: string
+      nullable: true
       pattern: '^36105[0-9]{9}$'
       example: '36105010362304'
     Title:

spec/cocina/models/validator_spec.rb

@@ -62,7 +62,7 @@
     end
   end
 
-  context 'when a nil value is passed' do
+  context 'when a nil copyright value (nullable string) is passed' do
     let(:policy) do
       Cocina::Models::AdminPolicy.new(
         externalIdentifier: 'druid:bc123df4567',
@@ -82,6 +82,28 @@
     end
   end
 
+  context 'when a nil barcode value (nullable oneOf) is passed' do
+    let(:policy) do
+      Cocina::Models::DRO.new(
+        externalIdentifier: 'druid:bc123df4567',
+        label: 'My item',
+        type: Cocina::Models::Vocab.object,
+        version: 1,
+        administrative: {
+          hasAdminPolicy: 'druid:bc123df4567'
+        },
+        access: {},
+        identification: {
+          barcode: nil
+        }
+      )
+    end
+
+    it 'does not raise' do
+      expect(policy.externalIdentifier).to eq('druid:bc123df4567')
+    end
+  end
+
   describe 'when invalid' do
     let(:policy) do
       Cocina::Models::AdminPolicy.new(