Merge pull request #10144 from owncloud/issue/9972

Issue/9972 Fix issues with group and username `0`

lib/private/group/database.php

@@ -185,7 +185,7 @@ class OC_Group_Database extends OC_Group_Backend {
 	public function groupExists($gid) {
 		$query = OC_DB::prepare('SELECT `gid` FROM `*PREFIX*groups` WHERE `gid` = ?');
 		$result = $query->execute(array($gid))->fetchOne();
-		if ($result) {
+		if ($result !== false) {
 			return true;
 		}
 		return false;

lib/private/group/manager.php

@@ -126,7 +126,7 @@ class Manager extends PublicEmitter implements IGroupManager {
 	 * @return \OC\Group\Group
 	 */
 	public function createGroup($gid) {
-		if (!$gid) {
+		if ($gid === '' || is_null($gid)) {
 			return false;
 		} else if ($group = $this->get($gid)) {
 			return $group;

lib/private/user.php

@@ -337,7 +337,7 @@ class OC_User {
 	 * Checks if the user is logged in
 	 */
 	public static function isLoggedIn() {
-		if (\OC::$session->get('user_id') && self::$incognitoMode === false) {
+		if (\OC::$session->get('user_id') !== null && self::$incognitoMode === false) {
 			return self::userExists(\OC::$session->get('user_id'));
 		}
 		return false;

lib/private/user/session.php

@@ -106,7 +106,7 @@ class Session implements IUserSession, Emitter {
 			return $this->activeUser;
 		} else {
 			$uid = $this->session->get('user_id');
-			if ($uid) {
+			if ($uid !== null) {
 				$this->activeUser = $this->manager->get($uid);
 				return $this->activeUser;
 			} else {