Module development and code questions

I'm writing my first Drupal 8 module and on top of that my OO-fu is very weak. I've created a skeleton module and it works fine. Where I'm running in to problems is trying to make an admin page for settings. I'm using this as my guide: https://befused.com/drupal/drupal8-admin-form-guide. When I clear the cache, I get the following error in the logs "Error: Unsupported operand types in /var/www/html/drupal_2020/core/lib/Drupal/Core/Routing/RouteBuilder.php on line 163".

Hi, I'm using webform module in my drupal site. I want to download just the filtered submissions. I don't want to download all submissions. is there any way to do that ? 

https://www.drupal.org/project/content_parser

When starting the parser module, I get an error.

InvalidArgumentException: sink must not be a boolean in GuzzleHttp\Client->applyOptions() (line 384 of /home/admin/web/testdr.vpoltave.net/public_html/vendor/guzzlehttp/guzzle/src/Client.php).

Hi All,

I have updated the drupal version from drupal 8.6.15 to drupal 8.8.2 but when we submit the form I am facing the issue.

The website encountered an unexpected error. Please try again later.
Error: Class 'CSD\Marketo\Client' not found in Drupal\marketo_ma\Service\MarketoMaApiClient->getClient() (line 119 of modules/patched/marketo_ma/src/Service/MarketoMaApiClient.php).
 

Not sure how to fix the issue.

Thanks in advnace.

PHP 7 introduces group import declarations, however Drupal Coder reports an error when using them. Does anyone know where to file requests for updates to the Drupal coding standard, or if this discussion has already been had somewhere?

Hi, My client want to attach each webform created to specific user with role( Jury ). Then , when the user log in he see all his webforms and he can manage the submissions and set up note. e.g: I attach the webform (apply 1 ) to Alex , the webform (apply 2) to Jack. When Alex log in; he see the webform (apply 1) than he manage all submissions of apply 1 and set up a score or note for each one. How can I apply this scenario with the webform module in Drupal 8.