Fix type errors

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

lib/private/Collaboration/Collaborators/UserPlugin.php

@@ -178,7 +178,7 @@ class UserPlugin implements ISearchPlugin {
 				$this->shareeEnumerationFullMatch &&
 				$lowerSearch !== '' && (strtolower($uid) === $lowerSearch ||
 				strtolower($userDisplayName) === $lowerSearch ||
-				strtolower($userEmail) === $lowerSearch)
+				strtolower($userEmail ?? '') === $lowerSearch)
 			) {
 				if (strtolower($uid) === $lowerSearch) {
 					$foundUserById = true;

lib/private/User/Database.php

@@ -386,13 +386,14 @@ class Database extends ABackend implements
 			$row = $result->fetch();
 			$result->closeCursor();
 
-			$this->cache[$uid] = false;
-
 			// "uid" is primary key, so there can only be a single result
 			if ($row !== false) {
-				$this->cache[$uid]['uid'] = (string)$row['uid'];
-				$this->cache[$uid]['displayname'] = (string)$row['displayname'];
+				$this->cache[$uid] = [
+					'uid' => (string)$row['uid'],
+					'displayname' => (string)$row['displayname'],
+				];
 			} else {
+				$this->cache[$uid] = false;
 				return false;
 			}
 		}