fix: Prevent PHP warnings when optional CacheEntry attributes are unset

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Author: susnux

lib/private/Files/Cache/Cache.php

@@ -149,7 +149,7 @@ public function getNumericStorageId() {
 	 * get the stored metadata of a file or folder
 	 *
 	 * @param string | int $file either the path of a file or folder or the file id for a file or folder
-	 * @return ICacheEntry|false the cache entry as array of false if the file is not found in the cache
+	 * @return ICacheEntry|false the cache entry as array or false if the file is not found in the cache
 	 */
 	public function get($file) {
 		$query = $this->getQueryBuilder();

lib/private/Files/Cache/CacheEntry.php

@@ -114,15 +114,15 @@ public function isEncrypted() {
 	}
 
 	public function getMetadataEtag(): ?string {
-		return $this->data['metadata_etag'];
+		return $this->data['metadata_etag'] ?? null;
 	}
 
 	public function getCreationTime(): ?int {
-		return $this->data['creation_time'];
+		return $this->data['creation_time'] ?? null;
 	}
 
 	public function getUploadTime(): ?int {
-		return $this->data['upload_time'];
+		return $this->data['upload_time'] ?? null;
 	}
 
 	public function getData() {