diff --git a/package-lock.json b/package-lock.json
index 71e1923199..d0c073a297 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -16637,6 +16637,15 @@
         "mock-require": "^2.0.2"
       }
     },
+    "tslint-language-service": {
+      "version": "0.9.9",
+      "resolved": "https://registry.npmjs.org/tslint-language-service/-/tslint-language-service-0.9.9.tgz",
+      "integrity": "sha1-9UbcOEg5eeb7PPpZWErYUls61No=",
+      "dev": true,
+      "requires": {
+        "mock-require": "^2.0.2"
+      }
+    },
     "tsutils": {
       "version": "2.29.0",
       "resolved": "https://registry.npmjs.org/tsutils/-/tsutils-2.29.0.tgz",
diff --git a/src/common/models/timestampable.ts b/src/common/models/timestampable.ts
index 74f4083d89..054b7e8e91 100644
--- a/src/common/models/timestampable.ts
+++ b/src/common/models/timestampable.ts
@@ -6,6 +6,6 @@
 // ==LICENSE-END==
 
 export interface Timestampable {
-    createdAt: string; // ISO 8601 string
-    updatedAt: string; // ISO 8601 string
+    createdAt?: string; // ISO 8601 string
+    updatedAt?: string; // ISO 8601 string
 }
diff --git a/src/common/redux/states/logger.ts b/src/common/redux/states/logger.ts
index d54423950a..906e20583e 100644
--- a/src/common/redux/states/logger.ts
+++ b/src/common/redux/states/logger.ts
@@ -6,5 +6,5 @@
 // ==LICENSE-END==
 
 export interface LoggerState {
-    lastMessage: string;
+    lastMessage: string | null;
 }
diff --git a/src/common/services/opds.ts b/src/common/services/opds.ts
index f25c9eb2d8..3ca9ad743a 100644
--- a/src/common/services/opds.ts
+++ b/src/common/services/opds.ts
@@ -44,9 +44,12 @@ export class OPDSParser {
                         identifier: uuid.v4(),
                         title: entry.title,
                         description: entry.summary.content,
-                        authors: [],
-                        files: [],
+                        // authors: [],
+                        // files: [],
                     };
+                    // To satisfy the static TypeScript compiler checks (strictNullChecks)
+                    publication.authors = [];
+                    publication.files = [];
 
                     // Fill authors
                     for (const author of entry.authors) {
diff --git a/src/main/api/publication.ts b/src/main/api/publication.ts
index 81c80c7771..a88d658fef 100644
--- a/src/main/api/publication.ts
+++ b/src/main/api/publication.ts
@@ -123,7 +123,9 @@ export class PublicationApi {
 
         for (const path of paths) {
             const newDoc = await this.catalogService.importFile(path);
-            newDocs.push(newDoc);
+            if (newDoc) {
+                newDocs.push(newDoc);
+            }
         }
 
         return newDocs.map((doc) => {
diff --git a/src/main/api/reader.ts b/src/main/api/reader.ts
index b7ee82042b..0bd948a0cd 100644
--- a/src/main/api/reader.ts
+++ b/src/main/api/reader.ts
@@ -54,7 +54,7 @@ export class ReaderApi {
         return this.locatorViewConverter.convertDocumentToView(savedDoc);
     }
 
-    public async getLastReadingLocation(data: any): Promise<LocatorView> {
+    public async getLastReadingLocation(data: any): Promise<LocatorView | null> {
         const { publication } = data;
         const docs = await this.locatorRepository.findByPublicationIdentifierAndLocatorType(
             publication.identifier,
diff --git a/src/main/converter/opds.ts b/src/main/converter/opds.ts
index 180e1dcb2f..9101713731 100644
--- a/src/main/converter/opds.ts
+++ b/src/main/converter/opds.ts
@@ -26,6 +26,8 @@ import { OPDSPublication } from "@r2-opds-js/opds/opds2/opds2-publication";
 // Logger
 const debug = debug_("readium-desktop:main#services/lcp");
 
+import { CoverView } from "readium-desktop/common/views/publication";
+
 @injectable()
 export class OpdsFeedViewConverter {
     public convertDocumentToView(document: OpdsFeedDocument): OpdsFeedView {
@@ -46,7 +48,7 @@ export class OpdsFeedViewConverter {
         return  {
             title,
             url: link.Href,
-            publicationCount: (link.Children) ? link.Children.length : null,
+            publicationCount: (link.Children) ? link.Children.length : undefined,
         };
     }
 
@@ -61,13 +63,13 @@ export class OpdsFeedViewConverter {
             tags = metadata.Subject.map((subject) => convertMultiLangStringToString(subject.Name));
         }
 
-        let publishedAt = null;
+        let publishedAt: string | undefined;
 
         if (metadata.PublicationDate) {
             publishedAt = moment(metadata.PublicationDate).toISOString();
         }
 
-        let cover = null;
+        let cover: CoverView | undefined;
 
         if (publication.Images && publication.Images.length > 0) {
             cover = {
@@ -76,8 +78,8 @@ export class OpdsFeedViewConverter {
         }
 
         // Get odps entry
-        let url = null;
-        let sampleUrl = null;
+        let url: string | undefined;
+        let sampleUrl: string | undefined;
         const links = publication.Links.filter(
             (link: any) => {
                 return (link.TypeLink.indexOf(";type=entry;profile=opds-catalog") > 0);
@@ -94,7 +96,7 @@ export class OpdsFeedViewConverter {
             sampleUrl = sampleLinks[0].Href;
         }
 
-        let base64OpdsPublication = null;
+        let base64OpdsPublication: string | undefined;
         if (links.length > 0) {
             url = links[0].Href;
         } else {
@@ -142,7 +144,7 @@ export class OpdsFeedViewConverter {
             buyUrl: buyLink && buyLink.Href,
             borrowUrl: borrowLink && borrowLink.Href,
             subscribeUrl: subscribeLink && subscribeLink.Href,
-            hasSample: sampleUrl && true,
+            hasSample: (typeof sampleUrl !== "undefined") && true,
             base64OpdsPublication,
             isFree,
         };
diff --git a/src/main/db/document/publication.ts b/src/main/db/document/publication.ts
index ef425d868a..202ddc8995 100644
--- a/src/main/db/document/publication.ts
+++ b/src/main/db/document/publication.ts
@@ -14,12 +14,12 @@ import { IHttpGetResult } from "readium-desktop/common/utils/http";
 
 interface Resources {
     filePublication: string;
-    opdsPublication: string;
+    opdsPublication?: string;
 }
 
 export interface PublicationDocument extends Identifiable, Timestampable {
     resources: Resources;
-    opdsPublication: any;
+    opdsPublication?: any;
     title: string;
     tags?: string[];
     files?: File[];
diff --git a/src/main/redux/sagas/i18n.ts b/src/main/redux/sagas/i18n.ts
index cb1bd600b3..88d8244198 100644
--- a/src/main/redux/sagas/i18n.ts
+++ b/src/main/redux/sagas/i18n.ts
@@ -13,6 +13,8 @@ import { all, call, take } from "redux-saga/effects";
 
 import { I18NState } from "readium-desktop/common/redux/states/i18n";
 
+import { I18NState } from "readium-desktop/common/redux/states/i18n";
+
 export function* localeWatcher() {
     while (true) {
         const action: i18nActions.ActionLocale = yield take(i18nActions.ActionType.Set);
diff --git a/src/main/services/catalog.ts b/src/main/services/catalog.ts
index 3766b62974..1a36cb62a2 100644
--- a/src/main/services/catalog.ts
+++ b/src/main/services/catalog.ts
@@ -56,7 +56,7 @@ export class CatalogService {
     @inject("publication-repository")
     private readonly publicationRepository!: PublicationRepository;
 
-    public async importFile(filePath: string, isLcpFile?: boolean): Promise<PublicationDocument> {
+    public async importFile(filePath: string, isLcpFile?: boolean): Promise<PublicationDocument | null> {
         const ext = path.extname(filePath);
 
         if (ext === ".lcpl" || (ext === ".part" && isLcpFile)) {
@@ -65,7 +65,7 @@ export class CatalogService {
             return this.importEpubFile(filePath);
         }
 
-        return null;
+        return Promise.resolve(null);
     }
 
     public async importOpdsEntry(url: string, downloadSample: boolean): Promise<THttpGetPublicationDocument> {
@@ -156,6 +156,9 @@ export class CatalogService {
         debug("[END] Download publication", downloadUrl, newDownload);
         // Import downloaded publication in catalog
         let publicationDocument = await this.importFile(download.dstPath, isLcpFile);
+        if (!publicationDocument) {
+            return Promise.reject("!publicationDocument");
+        }
 
         // Add opds publication serialization to resources
         const jsonOpdsPublication = TAJSON.serialize(opdsPublication);
@@ -200,6 +203,9 @@ export class CatalogService {
      * @return: Refreshed publication
      */
     public async refreshPublicationMetadata(publication: Publication) {
+        if (!publication.files) {
+            return;
+        }
         const pubPath = path.join(
             this.publicationStorage.getRootPath(),
             publication.files[0].url.substr(6),
@@ -238,7 +244,7 @@ export class CatalogService {
         const lcpl = JSON.parse(buffer.toString());
 
         // search the path of the epub file
-        let download: Download = null;
+        let download: Download | undefined;
 
         if (lcpl.links) {
             for (const link of lcpl.links) {
@@ -280,18 +286,18 @@ export class CatalogService {
             .from(JSON.stringify(jsonParsedPublication))
             .toString("base64");
 
-        const pubDocument = {
+        const pubDocument: PublicationDocument = {
             identifier: uuid.v4(),
             resources: {
                 filePublication: b64ParsedPublication,
-                opdsPublication: null,
+                opdsPublication: undefined,
             },
             title: convertMultiLangStringToString(parsedPublication.Metadata.Title),
             tags: [],
-            files: [],
-            coverFile: null,
-            customCover: null,
-        } as PublicationDocument;
+            coverFile: undefined,
+            customCover: undefined,
+        };
+        pubDocument.files = [];
 
         // Store publication on filesystem
         debug("[START] Store publication on filesystem", filePath);
diff --git a/src/main/services/lcp.ts b/src/main/services/lcp.ts
index fd67e92644..becd496202 100644
--- a/src/main/services/lcp.ts
+++ b/src/main/services/lcp.ts
@@ -98,7 +98,7 @@ export class LcpManager {
 
         debug("Parse publication - START", epubPath);
         const parsedPublication: Epub = await EpubParsePromise(epubPath);
-        let lcpInfo: LcpInfo = null;
+        let lcpInfo: LcpInfo | undefined;
 
         if (parsedPublication.LCP) {
             // Add Lcp info
@@ -286,7 +286,7 @@ export class LcpManager {
         lsdStatus: any,
     ): Promise<THttpGetPublicationDocument> {
         // Search LCPL license url
-        let lcplUrl: string = null;
+        let lcplUrl: string | undefined;
 
         for (const link of lsdStatus.links) {
             if (link.rel === "license") {
diff --git a/src/renderer/components/dialog/SameFileImportConfirm.tsx b/src/renderer/components/dialog/SameFileImportConfirm.tsx
index fcb97c3949..6d136746e3 100644
--- a/src/renderer/components/dialog/SameFileImportConfirm.tsx
+++ b/src/renderer/components/dialog/SameFileImportConfirm.tsx
@@ -52,6 +52,9 @@ class SameFileImportConfirm extends React.Component<Props> {
     }
 
     private addToCatalog() {
+        if (!this.props.importOpdsEntry) {
+            return;
+        }
         this.props.importOpdsEntry(
             {
                 url: this.props.publication.url,
diff --git a/tsconfig.json b/tsconfig.json
index 4ff9a3f692..cf77bfdd3b 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -15,6 +15,8 @@
     "noImplicitAny": true,
     "noImplicitThis": true,
     "alwaysStrict": true,
+    "strictNullChecks": true,
+    "strictPropertyInitialization": true,
     "strictFunctionTypes": true,
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,