diff --git a/lib/private/URLGenerator.php b/lib/private/URLGenerator.php
index f7d80d41b4fa6..c72c225517974 100644
--- a/lib/private/URLGenerator.php
+++ b/lib/private/URLGenerator.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -34,12 +35,10 @@
 
 namespace OC;
 
-
 use OCP\ICacheFactory;
 use OCP\IConfig;
 use OCP\IRequest;
 use OCP\IURLGenerator;
-use OCP\Route\IRoute;
 use RuntimeException;
 
 /**
@@ -74,10 +73,9 @@ public function __construct(IConfig $config,
 	 *
 	 * Returns a url to the given route.
 	 */
-	public function linkToRoute($route, $parameters = array()) {
+	public function linkToRoute(string $route, array $parameters = array()): string {
 		// TODO: mock router
-		$urlLinkTo = \OC::$server->getRouter()->generate($route, $parameters);
-		return $urlLinkTo;
+		return \OC::$server->getRouter()->generate($route, $parameters);
 	}
 
 	/**
@@ -88,7 +86,7 @@ public function linkToRoute($route, $parameters = array()) {
 	 *
 	 * Returns an absolute url to the given route.
 	 */
-	public function linkToRouteAbsolute($routeName, $arguments = array()) {
+	public function linkToRouteAbsolute(string $routeName, array $arguments = array()): string {
 		return $this->getAbsoluteURL($this->linkToRoute($routeName, $arguments));
 	}
 
@@ -102,20 +100,20 @@ public function linkToRouteAbsolute($routeName, $arguments = array()) {
 	 *
 	 * Returns a url to the given app and file.
 	 */
-	public function linkTo( $app, $file, $args = array() ) {
+	public function linkTo(string $app, string $file, array $args = array()): string {
 		$frontControllerActive = ($this->config->getSystemValue('htaccess.IgnoreFrontController', false) === true || getenv('front_controller_active') === 'true');
 
-		if( $app != '' ) {
+		if( $app !== '' ) {
 			$app_path = \OC_App::getAppPath($app);
 			// Check if the app is in the app folder
 			if ($app_path && file_exists($app_path . '/' . $file)) {
-				if (substr($file, -3) == 'php') {
+				if (substr($file, -3) === 'php') {
 
 					$urlLinkTo = \OC::$WEBROOT . '/index.php/apps/' . $app;
 					if ($frontControllerActive) {
 						$urlLinkTo = \OC::$WEBROOT . '/apps/' . $app;
 					}
-					$urlLinkTo .= ($file != 'index.php') ? '/' . $file : '';
+					$urlLinkTo .= ($file !== 'index.php') ? '/' . $file : '';
 				} else {
 					$urlLinkTo = \OC_App::getAppWebPath($app) . '/' . $file;
 				}
@@ -150,7 +148,7 @@ public function linkTo( $app, $file, $args = array() ) {
 	 *
 	 * Returns the path to the image.
 	 */
-	public function imagePath($app, $image) {
+	public function imagePath(string $app, string $image): string {
 		$cache = $this->cacheFactory->createDistributed('imagePath-'.md5($this->getBaseUrl()).'-');
 		$cacheKey = $app.'-'.$image;
 		if($key = $cache->get($cacheKey)) {
@@ -210,9 +208,9 @@ public function imagePath($app, $image) {
 		if($path !== '') {
 			$cache->set($cacheKey, $path);
 			return $path;
-		} else {
-			throw new RuntimeException('image not found: image:' . $image . ' webroot:' . \OC::$WEBROOT . ' serverroot:' . \OC::$SERVERROOT);
 		}
+
+		throw new RuntimeException('image not found: image:' . $image . ' webroot:' . \OC::$WEBROOT . ' serverroot:' . \OC::$SERVERROOT);
 	}
 
 
@@ -221,15 +219,15 @@ public function imagePath($app, $image) {
 	 * @param string $url the url in the ownCloud host
 	 * @return string the absolute version of the url
 	 */
-	public function getAbsoluteURL($url) {
+	public function getAbsoluteURL(string $url): string {
 		$separator = $url[0] === '/' ? '' : '/';
 
-		if (\OC::$CLI && !defined('PHPUNIT_RUN')) {
+		if (\OC::$CLI && !\defined('PHPUNIT_RUN')) {
 			return rtrim($this->config->getSystemValue('overwrite.cli.url'), '/') . '/' . ltrim($url, '/');
 		}
 		// The ownCloud web root can already be prepended.
-		if(substr($url, 0, strlen(\OC::$WEBROOT)) === \OC::$WEBROOT) {
-			$url = substr($url, strlen(\OC::$WEBROOT));
+		if(substr($url, 0, \strlen(\OC::$WEBROOT)) === \OC::$WEBROOT) {
+			$url = substr($url, \strlen(\OC::$WEBROOT));
 		}
 
 		return $this->getBaseUrl() . $separator . $url;
@@ -239,7 +237,7 @@ public function getAbsoluteURL($url) {
 	 * @param string $key
 	 * @return string url to the online documentation
 	 */
-	public function linkToDocs($key) {
+	public function linkToDocs(string $key): string {
 		$theme = \OC::$server->getThemingDefaults();
 		return $theme->buildDocLinkToKey($key);
 	}
@@ -247,7 +245,7 @@ public function linkToDocs($key) {
 	/**
 	 * @return string base url of the current request
 	 */
-	public function getBaseUrl() {
+	public function getBaseUrl(): string {
 		return $this->request->getServerProtocol() . '://' . $this->request->getServerHost() . \OC::$WEBROOT;
 	}
 }
diff --git a/lib/public/IURLGenerator.php b/lib/public/IURLGenerator.php
index 944029914e805..ebf35967551cc 100644
--- a/lib/public/IURLGenerator.php
+++ b/lib/public/IURLGenerator.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -24,14 +25,6 @@
  *
  */
 
-/**
- * Public interface of ownCloud for apps to use.
- * URL generator interface
- *
- */
-
-// use OCP namespace for all classes that are considered public.
-// This means that they should be used by apps instead of the internal ownCloud classes
 namespace OCP;
 
 /**
@@ -46,7 +39,7 @@ interface IURLGenerator {
 	 * @return string the url
 	 * @since 6.0.0
 	 */
-	public function linkToRoute($routeName, $arguments = array());
+	public function linkToRoute(string $routeName, array $arguments = array()): string;
 
 	/**
 	 * Returns the absolute URL for a route
@@ -55,7 +48,7 @@ public function linkToRoute($routeName, $arguments = array());
 	 * @return string the absolute url
 	 * @since 8.0.0
 	 */
-	public function linkToRouteAbsolute($routeName, $arguments = array());
+	public function linkToRouteAbsolute(string $routeName, array $arguments = array()): string;
 
 	/**
 	 * Returns an URL for an image or file
@@ -66,7 +59,7 @@ public function linkToRouteAbsolute($routeName, $arguments = array());
 	 * @return string the url
 	 * @since 6.0.0
 	 */
-	public function linkTo($appName, $file, $args = array());
+	public function linkTo(string $appName, string $file, array $args = array()): string;
 
 	/**
 	 * Returns the link to an image, like linkTo but only with prepending img/
@@ -75,7 +68,7 @@ public function linkTo($appName, $file, $args = array());
 	 * @return string the url
 	 * @since 6.0.0
 	 */
-	public function imagePath($appName, $file);
+	public function imagePath(string $appName, string $file): string;
 
 
 	/**
@@ -84,18 +77,18 @@ public function imagePath($appName, $file);
 	 * @return string the absolute version of the url
 	 * @since 6.0.0
 	 */
-	public function getAbsoluteURL($url);
+	public function getAbsoluteURL(string $url): string;
 
 	/**
 	 * @param string $key
 	 * @return string url to the online documentation
 	 * @since 8.0.0
 	 */
-	public function linkToDocs($key);
+	public function linkToDocs(string $key): string;
 
 	/**
 	 * @return string base url of the current request
 	 * @since 13.0.0
 	 */
-	public function getBaseUrl();
+	public function getBaseUrl(): string;
 }
diff --git a/tests/Settings/Mailer/NewUserMailHelperTest.php b/tests/Settings/Mailer/NewUserMailHelperTest.php
index 84553cc9007cb..6d6c6bf15c634 100644
--- a/tests/Settings/Mailer/NewUserMailHelperTest.php
+++ b/tests/Settings/Mailer/NewUserMailHelperTest.php
@@ -60,6 +60,8 @@ public function setUp() {
 		parent::setUp();
 
 		$this->defaults = $this->createMock(Defaults::class);
+		$this->defaults->method('getLogo')
+			->willReturn('myLogo');
 		$this->urlGenerator = $this->createMock(IURLGenerator::class);
 		$this->l10n = $this->createMock(IL10N::class);
 		$this->mailer = $this->createMock(IMailer::class);