Make password nullable in LoginData

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/private/Authentication/Login/LoginData.php

 
 	public function __construct(IRequest $request,
 								string $username,
-								string $password,
+								?string $password,
 								string $redirectUrl = null,
 								string $timeZone = '',
 								string $timeZoneOffset = '') {
 		return $this->username;
 	}
 
-	public function getPassword(): string {
+	public function getPassword(): ?string {
 		return $this->password;
 	}