GET form throws type error on rendering

[jtojnar]

Version: 3.0.0

After I updated to Nette 3, the GET forms no longer render.

You can reproduce it easily by minor tweak of the test:

--- a/tests/UI/Form.phpt
+++ b/tests/UI/Form.phpt
@@ -22,4 +22,6 @@
 	$presenter = new TestPresenter;
 	$form = new UI\Form($presenter, 'name');
 	$form->setMethod($form::GET); // must not throw exception
+
+	Assert::contains('<form', (string) $form);
 });

Running the test produces the following type error with PHP 7.2.18:

-- FAILED: Nette\Application\UI\Form | Form.phpt
   Exited with error code 255 (expected 0)
   E_USER_ERROR: Exception in Nette\Forms\Form::__toString(): parse_url() expects parameter 1 to be string, object given in /home/jtojnar/Projects/nette-application/vendor/nette/forms/src/Forms/Rendering/DefaultFormRenderer.php:170
   
   in src/Forms/Form.php(625) 
   in src/Forms/Form.php(625) trigger_error()
   in tests/UI/Form.phpt(26) Nette\Forms\Form->__toString()
   in nette-application/tests/bootstrap.php(27) {closure}()
   in tests/UI/Form.phpt(27) test()

It is weird, as the relevant code did not change in recent history:

https://github.com/nette/forms/blame/v3.0.0/src/Forms/Rendering/DefaultFormRenderer.php#L170
https://github.com/nette/application/blame/v3.0.0/src/Application/UI/Form.php#L45

[jtojnar]

I am proposing one possible solution in nette/forms#222