diff --git a/src/Core/Manifest/ModuleResourceLoader.php b/src/Core/Manifest/ModuleResourceLoader.php
index 96cf80e2c..6ae4ef3db 100644
--- a/src/Core/Manifest/ModuleResourceLoader.php
+++ b/src/Core/Manifest/ModuleResourceLoader.php
@@ -19,7 +19,7 @@ class ModuleResourceLoader implements TemplateGlobalProvider
      * For other files, return original value
      *
      * @param string $resource
-     * @return string
+     * @return string|null
      */
     public function resolvePath($resource)
     {
@@ -38,7 +38,7 @@ class ModuleResourceLoader implements TemplateGlobalProvider
      * Resolves resource specifier to the given url.
      *
      * @param string $resource
-     * @return string
+     * @return string|null
      */
     public function resolveURL($resource)
     {
@@ -60,7 +60,7 @@ class ModuleResourceLoader implements TemplateGlobalProvider
      * Template wrapper for resolvePath
      *
      * @param string $resource
-     * @return string
+     * @return string|null
      */
     public static function resourcePath($resource)
     {
@@ -71,7 +71,7 @@ class ModuleResourceLoader implements TemplateGlobalProvider
      * Template wrapper for resolveURL
      *
      * @param string $resource
-     * @return string
+     * @return string|null
      */
     public static function resourceURL($resource)
     {