Use !== instead of empty

Users can be named null

core/Controller/LoginController.php

@@ -74,7 +74,7 @@ class LoginController extends Controller {
 	 *
 	 * @return TemplateResponse
 	 */
-	public function showLoginForm($user,
+	public function showLoginForm($user = '',
 								  $redirect_url,
 								  $remember_login) {
 		if($this->userSession->isLoggedIn()) {
@@ -94,7 +94,7 @@ class LoginController extends Controller {
 		}
 
 		$parameters['messages'] = $messages;
-		if (!empty($user)) {
+		if ($user !== '') {
 			$parameters['username'] = $user;
 			$parameters['user_autofocus'] = false;
 		} else {
@@ -107,7 +107,7 @@ class LoginController extends Controller {
 
 		$parameters['canResetPassword'] = true;
 		if (!$this->config->getSystemValue('lost_password_link')) {
-			if (!empty($user)) {
+			if ($user !== '') {
 				$userObj = $this->userManager->get($user);
 				if ($userObj instanceof IUser) {
 					$parameters['canResetPassword'] = $userObj->canChangePassword();
@@ -119,7 +119,7 @@ class LoginController extends Controller {
 		$parameters['rememberLoginAllowed'] = \OC_Util::rememberLoginAllowed();
 		$parameters['rememberLoginState'] = !empty($remember_login) ? $remember_login : 0;
 
-		if (!empty($user)) {
+		if ($user !== '') {
 			$parameters['username'] = $user;
 			$parameters['user_autofocus'] = false;
 		} else {

tests/core/controller/LoginControllerTest.php

@@ -173,4 +173,42 @@ class LoginControllerTest extends TestCase {
 		);
 		$this->assertEquals($expectedResponse, $this->loginController->showLoginForm('LdapUser', '', ''));
 	}
+
+	public function testShowLoginFormForUserNamedNull() {
+		$this->userSession
+			->expects($this->once())
+			->method('isLoggedIn')
+			->willReturn(false);
+		$this->config
+			->expects($this->once())
+			->method('getSystemValue')
+			->with('lost_password_link')
+			->willReturn(false);
+		$user = $this->getMock('\\OCP\\IUser');
+		$user
+			->expects($this->once())
+			->method('canChangePassword')
+			->willReturn(false);
+		$this->userManager
+			->expects($this->once())
+			->method('get')
+			->with('0')
+			->willReturn($user);
+
+		$expectedResponse = new TemplateResponse(
+			'core',
+			'login',
+			[
+				'messages' => [],
+				'username' => '0',
+				'user_autofocus' => false,
+				'canResetPassword' => false,
+				'alt_login' => [],
+				'rememberLoginAllowed' => \OC_Util::rememberLoginAllowed(),
+				'rememberLoginState' => 0,
+			],
+			'guest'
+		);
+		$this->assertEquals($expectedResponse, $this->loginController->showLoginForm('0', '', ''));
+	}
 }