core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php b/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php
index 0a61193..9b4eb0d 100644
--- a/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php
@@ -30,6 +30,9 @@ public function getContext($query_arg = NULL) {
     elseif ($this->requestStack->getCurrentRequest()->query->has($query_arg)) {
       return $this->requestStack->getCurrentRequest()->query->get($query_arg) ?: '?valueless?';
     }
+    else {
+      return NULL;
+    }
   }
 
   /**