diff --git a/shared/test/Contributor.test.ts b/shared/test/Contributor.test.ts
index da6df4e0..19b8e7e7 100644
--- a/shared/test/Contributor.test.ts
+++ b/shared/test/Contributor.test.ts
@@ -163,7 +163,7 @@ describe('Contributor Tests', () => {
         name: new LocalizedString('Colin Greenwood'),
       }).serialize()
     ).toEqual({
-      name: { undefined: 'Colin Greenwood' },
+      name: { und: 'Colin Greenwood' },
     });
   });
 
@@ -187,8 +187,8 @@ describe('Contributor Tests', () => {
         ]),
       }).serialize()
     ).toEqual({
-      name: { undefined: 'Colin Greenwood' },
-      sortAs: { undefined: 'greenwood' },
+      name: { und: 'Colin Greenwood' },
+      sortAs: { und: 'greenwood' },
       identifier: 'colin',
       altIdentifier: [{ scheme: 'http://example.com/author-id', value: 'author-22222' }],
       role: ['bassist'],
@@ -211,7 +211,7 @@ describe('Contributor Tests', () => {
       ]).serialize()
     ).toEqual([
       {
-        name: { undefined: 'Thom Yorke' },
+        name: { und: 'Thom Yorke' },
       },
       {
         name: { en: 'Jonny Greenwood', fr: 'Jean Boisvert' },
diff --git a/shared/test/LocalizedString.test.ts b/shared/test/LocalizedString.test.ts
index bc936f51..45fdbf17 100644
--- a/shared/test/LocalizedString.test.ts
+++ b/shared/test/LocalizedString.test.ts
@@ -33,7 +33,7 @@ describe('LocalizedString Tests', () => {
 
   it('get JSON with one translation and no language', () => {
     expect(new LocalizedString('a string').serialize()).toEqual({
-      undefined: 'a string',
+      und: 'a string',
     });
   });
 
@@ -42,12 +42,12 @@ describe('LocalizedString Tests', () => {
       new LocalizedString({
         en: 'a string',
         fr: 'une chaîne',
-        undefined: 'bir metin',
+        und: 'bir metin',
       }).serialize()
     ).toEqual({
       en: 'a string',
       fr: 'une chaîne',
-      undefined: 'bir metin',
+      und: 'bir metin',
     });
   });
 
@@ -74,7 +74,7 @@ describe('LocalizedString Tests', () => {
       new LocalizedString({
         foo: 'a string',
         bar: 'une chaîne',
-        undefined: 'Surgh',
+        und: 'Surgh',
       }).getTranslation()
     ).toEqual('Surgh');
   });
diff --git a/shared/test/Manifest.test.ts b/shared/test/Manifest.test.ts
index ea1951c3..b7485c5f 100644
--- a/shared/test/Manifest.test.ts
+++ b/shared/test/Manifest.test.ts
@@ -136,7 +136,7 @@ describe('Manifest Tests', () => {
         readingOrder: new Links([]),
       }).serialize()
     ).toEqual({
-      metadata: { title: { undefined: 'Title' } },
+      metadata: { title: { und: 'Title' } },
       links: [],
       readingOrder: [],
     });
@@ -177,7 +177,7 @@ describe('Manifest Tests', () => {
       }).serialize()
     ).toEqual({
       '@context': ['https://readium.org/webpub-manifest/context.jsonld'],
-      metadata: { title: { undefined: 'Title' } },
+      metadata: { title: { und: 'Title' } },
       links: [{ href: '/manifest.json', rel: ['self'] }],
       readingOrder: [{ href: '/chap1.html', type: 'text/html' }],
       resources: [{ href: '/image.png', type: 'image/png' }],
diff --git a/shared/test/Metadata.test.ts b/shared/test/Metadata.test.ts
index a7ec9dde..2c806369 100644
--- a/shared/test/Metadata.test.ts
+++ b/shared/test/Metadata.test.ts
@@ -255,7 +255,7 @@ describe('Metadata Tests', () => {
         title: new LocalizedString('Title'),
       }).serialize()
     ).toEqual({
-      title: { undefined: 'Title' },
+      title: { und: 'Title' },
     });
   });
 
@@ -393,31 +393,31 @@ describe('Metadata Tests', () => {
       language: ['en', 'fr'],
       sortAs: { en: 'sort key', fr: 'clé de tri' },
       subject: [
-        { name: { undefined: 'Science Fiction' } },
-        { name: { undefined: 'Fantasy' } },
+        { name: { und: 'Science Fiction' } },
+        { name: { und: 'Fantasy' } },
       ],
-      author: [{ name: { undefined: 'Author' } }],
-      translator: [{ name: { undefined: 'Translator' } }],
-      editor: [{ name: { undefined: 'Editor' } }],
-      artist: [{ name: { undefined: 'Artist' } }],
-      illustrator: [{ name: { undefined: 'Illustrator' } }],
-      letterer: [{ name: { undefined: 'Letterer' } }],
-      penciler: [{ name: { undefined: 'Penciler' } }],
-      colorist: [{ name: { undefined: 'Colorist' } }],
-      inker: [{ name: { undefined: 'Inker' } }],
-      narrator: [{ name: { undefined: 'Narrator' } }],
-      contributor: [{ name: { undefined: 'Contributor' } }],
-      publisher: [{ name: { undefined: 'Publisher' } }],
-      imprint: [{ name: { undefined: 'Imprint' } }],
+      author: [{ name: { und: 'Author' } }],
+      translator: [{ name: { und: 'Translator' } }],
+      editor: [{ name: { und: 'Editor' } }],
+      artist: [{ name: { und: 'Artist' } }],
+      illustrator: [{ name: { und: 'Illustrator' } }],
+      letterer: [{ name: { und: 'Letterer' } }],
+      penciler: [{ name: { und: 'Penciler' } }],
+      colorist: [{ name: { und: 'Colorist' } }],
+      inker: [{ name: { und: 'Inker' } }],
+      narrator: [{ name: { und: 'Narrator' } }],
+      contributor: [{ name: { und: 'Contributor' } }],
+      publisher: [{ name: { und: 'Publisher' } }],
+      imprint: [{ name: { und: 'Imprint' } }],
       layout: 'fixed',
       readingProgression: 'rtl',
       description: 'Description',
       duration: 4.24,
       numberOfPages: 240,
       belongsTo: {
-        collection: [{ name: { undefined: 'Collection' } }],
-        series: [{ name: { undefined: 'Series' } }],
-        'schema:Periodical': [{ name: { undefined: 'Periodical' } }],
+        collection: [{ name: { und: 'Collection' } }],
+        series: [{ name: { und: 'Series' } }],
+        'schema:Periodical': [{ name: { und: 'Periodical' } }],
       },
       tdm: {
         reservation: 'all',
@@ -451,7 +451,7 @@ describe('Metadata Tests', () => {
         title: new LocalizedString('Title'),
       }).serialize()
     ).toEqual({
-      title: { undefined: 'Title' }
+      title: { und: 'Title' }
     });
   });
 
diff --git a/shared/test/Subject.test.ts b/shared/test/Subject.test.ts
index 3a7dc4e0..202f56e2 100644
--- a/shared/test/Subject.test.ts
+++ b/shared/test/Subject.test.ts
@@ -124,7 +124,7 @@ describe('Subject Tests', () => {
         name: new LocalizedString('Science Fiction'),
       }).serialize()
     ).toEqual({
-      name: { undefined: 'Science Fiction' },
+      name: { und: 'Science Fiction' },
     });
   });
 
@@ -141,8 +141,8 @@ describe('Subject Tests', () => {
         ]),
       }).serialize()
     ).toEqual({
-      name: { undefined: 'Science Fiction' },
-      sortAs: { undefined: 'science-fiction' },
+      name: { und: 'Science Fiction' },
+      sortAs: { und: 'science-fiction' },
       scheme: 'http://scheme',
       code: 'CODE',
       links: [{ href: 'pub1' }, { href: 'pub2' }],
@@ -160,10 +160,10 @@ describe('Subject Tests', () => {
       ]).serialize()
     ).toEqual([
       {
-        name: { undefined: 'Fantasy' },
+        name: { und: 'Fantasy' },
       },
       {
-        name: { undefined: 'Science Fiction' },
+        name: { und: 'Science Fiction' },
         scheme: 'http://scheme',
       },
     ]);