Fix cache key generation (remove slashes)

Cache/CacheWrapper.php

@@ -15,6 +15,17 @@ public function __construct(CacheService $cacheService)
         $this->cacheService = $cacheService;
     }
 
+    /**
+     * Remove slashes from start and end of keys, and for content replace it with _ to avoid issues for Stash.
+     *
+     * @param string $key
+     * @return string
+     */
+    private function washKey($key)
+    {
+        return str_replace('/', '_', trim($key, '/'));
+    }
+
     /**
      * @return bool
      */
@@ -42,7 +53,7 @@ public function clear()
     public function getItem($key)
     {
         if (is_array($key)) {
-            $key = implode('/', $key);
+            $key = implode('/', array_map([$this, 'washKey'], $key));
         }
 
         return $this->cacheService->getItem($key);