Steps to reproduce the issue

Example code:

            $regmodel = $this->getModel('Registration', 'UsersModel');
            $regdata = array(
                "name" => $data['name'],
                "username" => $data['username'],
                "password2" => $data['password2'],
                "password1" => $data['password1'],
                "email1" => $data['email1']
            );
            $return_uid = $regmodel->register($regdata);

Expected result

true

Actual result

Fatal error: Call to a member function setFieldAttribute() on boolean in components\com_users\models\registration.php on line 307

System information (as much as possible)

Start at version Joomla CMS 3.6.5

Additional comments

When I create a custom registration form with multi languages support I have this error.
Error only in latest version Joomla CMS 3.6.5 and only with multi languages support.
I think problem with this code(file components\com_users\models\registration.php):
a)Line 245

$form = $this->getForm(array(), false);

b)Line 305 - 308

if (JLanguageMultilang::isEnabled())
		{
			$form->setFieldAttribute('language', 'type', 'frontend_language', 'params');
		}

Sorry for my English !