diff --git a/lib/ACL/ACLCacheWrapper.php b/lib/ACL/ACLCacheWrapper.php
index 5eca89701..62c3da8bb 100644
--- a/lib/ACL/ACLCacheWrapper.php
+++ b/lib/ACL/ACLCacheWrapper.php
@@ -55,10 +55,9 @@ protected function formatCacheEntry($entry, array $rules = []) {
 	public function getFolderContentsById($fileId) {
 		$results = $this->getCache()->getFolderContentsById($fileId);
 		$rules = $this->preloadEntries($results);
-		$entries = array_map(function ($entry) use ($rules) {
+		return array_filter(array_map(function ($entry) use ($rules) {
 			return $this->formatCacheEntry($entry, $rules);
-		}, $results);
-		return array_filter(array_filter($entries));
+		}, $results));
 	}
 
 	public function search($pattern) {
diff --git a/lib/Command/ACL.php b/lib/Command/ACL.php
index f63859a8f..a36b23545 100644
--- a/lib/Command/ACL.php
+++ b/lib/Command/ACL.php
@@ -61,7 +61,7 @@ protected function configure() {
 
 	protected function execute(InputInterface $input, OutputInterface $output) {
 		$folder = $this->getFolder($input, $output);
-		if ($folder === false) {
+		if ($folder === null) {
 			return -1;
 		}
 		if ($input->getOption('enable')) {
diff --git a/lib/Command/Delete.php b/lib/Command/Delete.php
index 6c2c2e1c9..2a9026bde 100644
--- a/lib/Command/Delete.php
+++ b/lib/Command/Delete.php
@@ -26,7 +26,7 @@ protected function configure() {
 
 	protected function execute(InputInterface $input, OutputInterface $output) {
 		$folder = $this->getFolder($input, $output);
-		if ($folder === false) {
+		if ($folder === null) {
 			return -1;
 		}
 		$helper = $this->getHelper('question');
diff --git a/lib/Command/FolderCommand.php b/lib/Command/FolderCommand.php
index c4ac76b60..c3158445b 100644
--- a/lib/Command/FolderCommand.php
+++ b/lib/Command/FolderCommand.php
@@ -31,19 +31,19 @@ public function __construct(FolderManager $folderManager, IRootFolder $rootFolde
 	}
 
 	/**
-	 * @psalm-return array{id: mixed, mount_point: string, groups: array<empty, empty>|mixed, quota: int, size: int|mixed, acl: bool}|false
+	 * @psalm-return ?array{id: mixed, mount_point: string, groups: array<empty, empty>|mixed, quota: int, size: int|mixed, acl: bool}
 	 */
-	protected function getFolder(InputInterface $input, OutputInterface $output) {
+	protected function getFolder(InputInterface $input, OutputInterface $output): ?array {
 		$folderId = (int)$input->getArgument('folder_id');
 		if ((string)$folderId !== $input->getArgument('folder_id')) {
 			// Protect against removing folderId === 0 when typing a string (e.g. folder name instead of folder id)
 			$output->writeln('<error>Folder id argument is not an integer. Got ' . $input->getArgument('folder_id') . '</error>');
-			return false;
+			return null;
 		}
 		$folder = $this->folderManager->getFolder($folderId, $this->rootFolder->getMountPoint()->getNumericStorageId());
-		if ($folder === false) {
+		if ($folder === null) {
 			$output->writeln('<error>Folder not found: ' . $folderId . '</error>');
-			return false;
+			return null;
 		}
 		return $folder;
 	}
diff --git a/lib/Command/Group.php b/lib/Command/Group.php
index bd64ed64f..f8f5198ae 100644
--- a/lib/Command/Group.php
+++ b/lib/Command/Group.php
@@ -46,7 +46,7 @@ protected function configure() {
 
 	protected function execute(InputInterface $input, OutputInterface $output) {
 		$folder = $this->getFolder($input, $output);
-		if ($folder === false) {
+		if ($folder === null) {
 			return -1;
 		}
 
diff --git a/lib/Command/Quota.php b/lib/Command/Quota.php
index 5a5e46f57..9dcffa3a9 100644
--- a/lib/Command/Quota.php
+++ b/lib/Command/Quota.php
@@ -25,7 +25,7 @@ protected function configure() {
 
 	protected function execute(InputInterface $input, OutputInterface $output) {
 		$folder = $this->getFolder($input, $output);
-		if ($folder === false) {
+		if ($folder === null) {
 			return -1;
 		}
 		$quotaString = strtolower($input->getArgument('quota'));
diff --git a/lib/Command/Rename.php b/lib/Command/Rename.php
index 906f34573..a2e10a5df 100644
--- a/lib/Command/Rename.php
+++ b/lib/Command/Rename.php
@@ -24,7 +24,7 @@ protected function configure(): void {
 
 	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$folder = $this->getFolder($input, $output);
-		if ($folder === false) {
+		if ($folder === null) {
 			return -1;
 		}
 		$this->folderManager->renameFolder($folder['id'], $input->getArgument('name'));
diff --git a/lib/Command/Scan.php b/lib/Command/Scan.php
index 11f2ad0f7..9c17321bf 100644
--- a/lib/Command/Scan.php
+++ b/lib/Command/Scan.php
@@ -63,7 +63,7 @@ protected function execute(InputInterface $input, OutputInterface $output) {
 			$folders = $this->folderManager->getAllFolders();
 		} else {
 			$folder = $this->getFolder($input, $output);
-			if ($folder === false) {
+			if ($folder === null) {
 				return -1;
 			}
 			$folders = [$folder['id'] => $folder];
diff --git a/lib/Controller/FolderController.php b/lib/Controller/FolderController.php
index c869f2f7d..669ceadc2 100644
--- a/lib/Controller/FolderController.php
+++ b/lib/Controller/FolderController.php
@@ -133,7 +133,7 @@ private function checkFolderExists(int $id): ?DataResponse {
 			return new DataResponse([], Http::STATUS_NOT_FOUND);
 		}
 		$folder = $this->manager->getFolder($id, $storageId);
-		if ($folder === false) {
+		if ($folder === null) {
 			return new DataResponse([], Http::STATUS_NOT_FOUND);
 		}
 		return null;
@@ -152,7 +152,7 @@ private function getRootFolderStorageId(): ?int {
 	public function addFolder(string $mountpoint): DataResponse {
 		$id = $this->manager->createFolder(trim($mountpoint));
 		$folder = $this->manager->getFolder($id, $this->rootFolder->getMountPoint()->getNumericStorageId());
-		if ($folder === false) {
+		if ($folder === null) {
 			throw new OCSNotFoundException();
 		}
 		return new DataResponse($folder);
diff --git a/lib/Folder/FolderManager.php b/lib/Folder/FolderManager.php
index 9c6fa2040..019184de6 100644
--- a/lib/Folder/FolderManager.php
+++ b/lib/Folder/FolderManager.php
@@ -255,10 +255,10 @@ private function getManageAcl(array $mappings): array {
 	}
 
 	/**
-	 * @return array{id: mixed, mount_point: mixed, groups: array<string, array{displayName: string, type: string, permissions: integer}>, quota: int, size: int, acl: bool}|false
+	 * @return ?array{id: mixed, mount_point: mixed, groups: array<string, array{displayName: string, type: string, permissions: integer}>, quota: int, size: int, acl: bool}
 	 * @throws Exception
 	 */
-	public function getFolder(int $id, int $rootStorageId) {
+	public function getFolder(int $id, int $rootStorageId): ?array {
 		$applicableMap = $this->getAllApplicable();
 
 		$query = $this->connection->getQueryBuilder();
@@ -271,17 +271,20 @@ public function getFolder(int $id, int $rootStorageId) {
 		$result = $query->executeQuery();
 		$row = $result->fetch();
 		$result->closeCursor();
+		if (!$row) {
+			return null;
+		}
 
 		$folderMappings = $this->getFolderMappings($id);
-		return $row ? [
+		return [
 			'id' => $id,
 			'mount_point' => (string)$row['mount_point'],
 			'groups' => $applicableMap[$id] ?? [],
 			'quota' => (int)$row['quota'],
-			'size' => $row['size'] ? $row['size'] : 0,
+			'size' => $row['size'] ?: 0,
 			'acl' => (bool)$row['acl'],
 			'manage' => $this->getManageAcl($folderMappings)
-		] : false;
+		];
 	}
 
 	/**