diff --git a/src/amo/actions/reviews.js b/src/amo/actions/reviews.js
index 8164c5da5f7..4f9414f10bf 100644
--- a/src/amo/actions/reviews.js
+++ b/src/amo/actions/reviews.js
@@ -86,6 +86,7 @@ export function createInternalReview(
     reviewAddon: {
       iconUrl: review.addon.icon_url,
       id: review.addon.id,
+      // $FlowIgnore: the add-on's name cannot be falsey.
       name: selectLocalizedContent(review.addon.name, lang),
       slug: review.addon.slug,
     },
diff --git a/src/amo/components/HomepageShelves/index.js b/src/amo/components/HomepageShelves/index.js
index c5b4f0d1602..d77861e7f67 100644
--- a/src/amo/components/HomepageShelves/index.js
+++ b/src/amo/components/HomepageShelves/index.js
@@ -2,6 +2,7 @@
 import url from 'url';
 
 import * as React from 'react';
+import invariant from 'invariant';
 
 import LandingAddonsCard from 'amo/components/LandingAddonsCard';
 import LoadingText from 'amo/components/LoadingText';
@@ -68,6 +69,9 @@ export const HomepageShelvesBase = (props: InternalProps): React.Node => {
   } else {
     shelvesContent = shelves.map((shelf) => {
       const { addons, addonType, endpoint, footer, title, url: apiUrl } = shelf;
+
+      invariant(title, 'title is required');
+
       const shelfKey = title.replace(/\s/g, '-');
 
       const footerText = footer.text
diff --git a/src/amo/pages/AddonInfo/index.js b/src/amo/pages/AddonInfo/index.js
index a563d734b9c..15bdc7545e0 100644
--- a/src/amo/pages/AddonInfo/index.js
+++ b/src/amo/pages/AddonInfo/index.js
@@ -118,7 +118,7 @@ export class AddonInfoBase extends React.Component<InternalProps> {
       const needsLicenceText =
         addonVersion &&
         addonVersion.license &&
-        addonVersion.license.text === undefined;
+        addonVersion.license.text === null;
       if (
         addon &&
         addon.currentVersionId &&
diff --git a/src/amo/reducers/addons.js b/src/amo/reducers/addons.js
index 89b93ae078a..9bb36d5a248 100644
--- a/src/amo/reducers/addons.js
+++ b/src/amo/reducers/addons.js
@@ -195,7 +195,9 @@ export const selectLocalizedUrlWithOutgoing = (
 ): UrlWithOutgoing | null => {
   if (url && url.url && url.outgoing) {
     return {
+      // $FlowIgnore: this can't be `null` because we check before.
       url: selectLocalizedContent(url.url, lang),
+      // $FlowIgnore: this can't be `null` because we check before.
       outgoing: selectLocalizedContent(url.outgoing, lang),
     };
   }
@@ -234,6 +236,7 @@ export function createInternalAddon(
     last_updated: apiAddon.last_updated,
     latest_unlisted_version: apiAddon.latest_unlisted_version,
     locale_disambiguation: apiAddon.locale_disambiguation,
+    // $FlowIgnore: the add-on's name cannot be falsey.
     name: selectLocalizedContent(apiAddon.name, lang),
     previews: apiAddon.previews
       ? createInternalPreviews(apiAddon.previews, lang)
diff --git a/src/amo/reducers/autocomplete.js b/src/amo/reducers/autocomplete.js
index b119ec2dd02..689b7668808 100644
--- a/src/amo/reducers/autocomplete.js
+++ b/src/amo/reducers/autocomplete.js
@@ -29,7 +29,7 @@ export type ExternalSuggestion = {|
 export type SuggestionType = {|
   addonId: number,
   iconUrl: string,
-  name: string,
+  name: string | null,
   promoted: Array<PromotedType>,
   type: string,
   url: string,
diff --git a/src/amo/reducers/blocks.js b/src/amo/reducers/blocks.js
index 8c393790f80..57478c64183 100644
--- a/src/amo/reducers/blocks.js
+++ b/src/amo/reducers/blocks.js
@@ -24,7 +24,7 @@ export type ExternalBlockType = {|
 
 export type BlockType = {|
   ...ExternalBlockType,
-  name: string,
+  name: string | null,
 |};
 
 export type BlocksState = {|
diff --git a/src/amo/reducers/home.js b/src/amo/reducers/home.js
index 3c76104f167..cfb19e5c409 100644
--- a/src/amo/reducers/home.js
+++ b/src/amo/reducers/home.js
@@ -39,7 +39,7 @@ export type InternalPrimaryHeroShelfExternalAddonType = {|
   id: string,
   guid: string,
   homepage: UrlWithOutgoing | null,
-  name: string,
+  name: string | null,
   type: string,
 |};
 
@@ -116,18 +116,18 @@ export type ExternalSecondaryHeroShelfType = {|
 export type LinkWithTextType = {|
   url: string,
   outgoing: string,
-  text: string,
+  text: string | null,
 |};
 
 export type SecondaryHeroModuleType = {|
   icon: string,
-  description: string,
+  description: string | null,
   cta: LinkWithTextType | null,
 |};
 
 export type SecondaryHeroShelfType = {|
-  headline: string,
-  description: string,
+  headline: string | null,
+  description: string | null,
   cta: LinkWithTextType | null,
   modules: Array<SecondaryHeroModuleType>,
 |} | null;
@@ -152,7 +152,7 @@ export type ExternalResultShelfType = {|
 |};
 
 export type ResultShelfType = {|
-  title: string,
+  title: string | null,
   url: string,
   endpoint: string,
   addonType: AddonTypeType,
diff --git a/src/amo/reducers/utils.js b/src/amo/reducers/utils.js
index ed2c93537d5..f9cf4f2ebbd 100644
--- a/src/amo/reducers/utils.js
+++ b/src/amo/reducers/utils.js
@@ -1,14 +1,18 @@
+/* @flow */
 import invariant from 'invariant';
 
 import type { LocalizedString } from 'amo/types/api';
 
-import type { CategoryEntry } from './categories';
-import type { ExternalAddonType, PromotedType } from '../types/addons';
+import type {
+  ExternalAddonType,
+  PartialExternalAddonType,
+  PromotedType,
+} from '../types/addons';
 
 export const selectLocalizedContent = (
-  field: LocalizedString,
+  field: ?LocalizedString,
   lang: string,
-) => {
+): string | null => {
   invariant(lang, 'lang must not be empty');
   if (!field) {
     return null;
@@ -22,9 +26,9 @@ export const selectLocalizedContent = (
 };
 
 export const selectCategoryObject = (
-  apiAddon: ExternalAddonType,
-): CategoryEntry => {
-  return apiAddon.categories;
+  apiAddon: ExternalAddonType | PartialExternalAddonType,
+): Array<string> => {
+  return apiAddon.categories || [];
 };
 
 export const makeInternalPromoted = (
diff --git a/src/amo/reducers/versions.js b/src/amo/reducers/versions.js
index c6aca46308c..0e954dd023d 100644
--- a/src/amo/reducers/versions.js
+++ b/src/amo/reducers/versions.js
@@ -77,7 +77,7 @@ export type ExternalVersionLicenseType = {|
 
 type PartialVersionLicenseType = {|
   name: string | null,
-  text?: string,
+  text: string | null,
   url: string,
 |};
 
@@ -98,7 +98,7 @@ export type AddonVersionType = {
   isStrictCompatibilityEnabled: boolean,
   license: VersionLicenseType | null,
   file: AddonFileType | null,
-  releaseNotes?: string,
+  releaseNotes: string | null,
   version: string,
 };
 
@@ -146,7 +146,7 @@ export const createInternalVersion = (
           name: selectLocalizedContent(version.license.name, lang),
           text:
             version.license.text === undefined
-              ? undefined
+              ? null
               : selectLocalizedContent(version.license.text, lang),
           url: version.license.url,
         }
diff --git a/src/amo/types/addons.js b/src/amo/types/addons.js
index 36295027035..d9c2821deab 100644
--- a/src/amo/types/addons.js
+++ b/src/amo/types/addons.js
@@ -59,7 +59,7 @@ export type ExternalLanguageToolType = {|
 
 export type LanguageToolType = {|
   ...ExternalLanguageToolType,
-  name: string,
+  name: string | null,
 |};
 
 export type PromotedType = {|
@@ -83,7 +83,7 @@ export type PreviewType = {|
   thumbnail_h: number,
   thumbnail_src: string,
   thumbnail_w: number,
-  title: string,
+  title: string | null,
   w: number,
 |};
 
diff --git a/tests/unit/amo/reducers/test_versions.js b/tests/unit/amo/reducers/test_versions.js
index a4d9a606c8a..9d6201c4a0e 100644
--- a/tests/unit/amo/reducers/test_versions.js
+++ b/tests/unit/amo/reducers/test_versions.js
@@ -175,10 +175,10 @@ describe(__filename, () => {
       });
     });
 
-    it('returns undefined for license.text if it is missing from the response', () => {
+    it('returns null for license.text if it is missing from the response', () => {
       // fakeVersion does not include license.text.
       const version = createInternalVersion(fakeVersion, lang);
-      expect(version.license.text).toEqual(undefined);
+      expect(version.license.text).toEqual(null);
     });
 
     // See https://github.com/mozilla/addons-frontend/issues/11337