When a user clicks "reset password" it shows them this error

When ever a user clicks reset password it takes them to this error:

Fatal error: Uncaught Error: Call to a member function getName() on null in /homepages/22/d816395098/htdocs/forum/includes/functions.php:4087 Stack trace: #0 /homepages/22/d816395098/htdocs/forum/phpbb/controller/helper.php(89): page_header('Reset password', false, 0, 'forum', false) #1 /homepages/22/d816395098/htdocs/forum/phpbb/ucp/controller/reset_password.php(287): phpbb\controller\helper->render('ucp_reset_passw...', 'Reset password') #2 /homepages/22/d816395098/htdocs/forum/vendor/symfony/http-kernel/HttpKernel.php(151): phpbb\ucp\controller\reset_password->request() #3 /homepages/22/d816395098/htdocs/forum/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(phpbb\symfony_request), 1) #4 /homepages/22/d816395098/htdocs/forum/app.php(32): Symfony\Component\HttpKernel\HttpKernel->handle(Object(phpbb\symfony_request)) #5 {main} thrown in /homepages/22/d816395098/htdocs/forum/includes/functions.php on line 4087