Merge #261 [backport 28]fix: Avoid clear cache with prefix [maybe nee…

…ded for 29]

(cherry picked from commit 410e6d0)

lib/private/Collaboration/Reference/ReferenceManager.php

@@ -174,7 +174,7 @@ public function invalidateCache(string $cachePrefix, ?string $cacheKey = null):
 			return;
 		}
 
-		$this->cache->remove(md5($cachePrefix) . '-' . md5($cacheKey));
+		$this->cache->remove(md5($cachePrefix) . '-' . md5($cacheKey ?? ''));
 	}
 
 	/**