diff --git a/src/Plugin/Block/ReserveBlock.php b/src/Plugin/Block/ReserveBlock.php
index 82956d0..f56528c 100644
--- a/src/Plugin/Block/ReserveBlock.php
+++ b/src/Plugin/Block/ReserveBlock.php
@@ -21,7 +21,7 @@ class ReserveBlock extends BlockBase {
   public function build() {
     $html = $this->getReserves();
     if (empty($html)) {
-      return '';
+      return [];
     }
 
     return [