diff --git a/lib/Drupal/Component/Discovery/YamlDiscovery.php b/lib/Drupal/Component/Discovery/YamlDiscovery.php
index bf4ee15..1d147fd 100644
--- a/lib/Drupal/Component/Discovery/YamlDiscovery.php
+++ b/lib/Drupal/Component/Discovery/YamlDiscovery.php
@@ -48,7 +48,9 @@ public function __construct($name, array $directories) {
   public function findAll() {
     $all = array();
     foreach ($this->findFiles() as $provider => $file) {
-      $all[$provider] = Yaml::decode(file_get_contents($file));
+      // If a file is empty or its contents are commented out, return an empty
+      // array instead of NULL for type consistency.
+      $all[$provider] = Yaml::decode(file_get_contents($file)) ?: [];
     }
 
     return $all;