`submitForm` throws `TypeError` for input fields without `name` attribute

[Daniel Haupt]

Example form:

<form>
    <input type="text" name="username" />
    <input type="submit" value="Submit" />
</form>

When running this in an acceptance test:

$I->submitForm('form',['username' => 'Test']);

This error occurs:

[TypeError] Argument 1 passed to Codeception\Module\WebDriver::getSubmissionFormFieldName() must be of the type string, 
null given, 
called in /var/www/html/vendor/codeception/module-webdriver/src/Codeception/Module/WebDriver.php on line 2434

The error is thrown because of the missing name attribute from the submit input.

I've noticed the issue after updating from v1.4.0 to v2.0.0 (which introduced type safety). My test worked in v1.4.0.