Make DisplayNameCache return null if user doesn't exists

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

apps/files_sharing/lib/Cache.php

@@ -170,7 +170,7 @@ class Cache extends CacheJail {
 	private function getOwnerDisplayName() {
 		if (!$this->ownerDisplayName) {
 			$uid = $this->storage->getOwner('');
-			$this->ownerDisplayName = $this->displayNameCache->getDisplayName($uid);
+			$this->ownerDisplayName = $this->displayNameCache->getDisplayName($uid) ?? $uid;
 		}
 		return $this->ownerDisplayName;
 	}

lib/private/User/DisplayNameCache.php

@@ -47,7 +47,7 @@ class DisplayNameCache implements IEventListener {
 		$this->userManager = $userManager;
 	}
 
-	public function getDisplayName(string $userId) {
+	public function getDisplayName(string $userId): ?string {
 		if (isset($this->cache[$userId])) {
 			return $this->cache[$userId];
 		}
@@ -61,7 +61,7 @@ class DisplayNameCache implements IEventListener {
 		if ($user) {
 			$displayName = $user->getDisplayName();
 		} else {
-			$displayName = $userId;
+			$displayName = null;
 		}
 		$this->cache[$userId] = $displayName;
 		$this->memCache->set($userId, $displayName, 60 * 10); // 10 minutes

lib/private/User/LazyUser.php

@@ -51,7 +51,7 @@ class LazyUser implements IUser {
 	}
 
 	public function getDisplayName() {
-		return $this->userManager->getDisplayName($this->uid);
+		return $this->userManager->getDisplayName($this->uid) ?? $this->uid;
 	}
 
 	public function setDisplayName($displayName) {

lib/private/User/Manager.php

@@ -188,7 +188,7 @@ class Manager extends PublicEmitter implements IUserManager {
 		return null;
 	}
 
-	public function getDisplayName(string $uid): string {
+	public function getDisplayName(string $uid): ?string {
 		return $this->displayNameCache->getDisplayName($uid);
 	}
 

lib/public/IUserManager.php

@@ -87,13 +87,11 @@ interface IUserManager {
 	/**
 	 * Get the display name of a user
 	 *
-	 * Note that this will return the uid if the user is not found instead of throwing an exception
-	 *
 	 * @param string $uid
-	 * @return string
+	 * @return string|null
 	 * @since 25.0.0
 	 */
-	public function getDisplayName(string $uid): string;
+	public function getDisplayName(string $uid): ?string;
 
 	/**
 	 * check if a user exists