The "" plugin does not exist on config save in PolicyEditForm.php

It works for me and no one else has reported. Maybe it is related to something on your site? I suggest to test with creating policy for one of the Core modules.

Hi Adam,
I also tried with one of the core modules and it behaves the same

https://drive.google.com/file/d/1X7qqCv8DMaqXBZTSUGuKdzdOqpFZPy49/view?usp=sharing

I just completed a Drupal 10 upgrade and I'm getting this same error when I try to add a new element to an existing policy. It worked without problems during the entire development process, but now that I've pushed the upgrade to production it fails.

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "" plugin does not exist. Valid plugin IDs for Drupal\symfony_mailer\Processor\EmailAdjusterManager are: mailer_url_to_absolute, email_bcc, email_body, email_cc, mailer_default_headers, email_from, mailer_hooks, mailer_inline_css, email_plain, email_priority, email_reply_to, email_skip_sending, email_subject, email_theme, email_to, email_transport, mailer_wrap_and_convert in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 53 of /var/www/web/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php).

I should add that this is a policy for email receipts in Drupal Commerce.

The problem was competing form actions. There was $form['add_actions'] as type 'action' and then $form['actions'] as type 'action.
The $name variable was always empty (attached screenshot) when clicking the Save button, hence the error in this issue.
The solution was to make $form['add_actions'] a container within the existing $form['actions'].
Patch added.

Thanks. Drupal.org now uses requests instead of patches please.

Ok, done.

Please put your changes in the 3398364-the--plugin branch then create a merge request. This will cause the tests to run. Thanks.

I have changed patch into the MR, please review.

Thanks. For me the result is worse than before. Before the select and button were on the same line, and now they are one below the other - see screenshots attached.

I believe that the buttons are no longer in the container because they still have $form['add_actions']. Instead it worked for me like this:

    $form['add_actions'] = [
      '#type' => 'container',
      '#weight' => -1,
      '#attributes' => ['class' => ['container-inline']],
    ];

Please can you check if that still works for you, then update the MR?

I can confirm the above in #13 works fine!

Just needs a MR for the code in #13

I updated MR as per #13, Please review.

It looks good to me thanks. Please can anyone else test?

We need a MR against 2.x please as that is now the dev branch. I can also commit the 1.x one afterwards as a backport.

Added MR for 2.x branch.

Great thanks. Let's wait a week and see if someone will test, otherwise I can commit anyway based on #14.

I tried replicating this issue on Drupal 10 with module version 2.x, following the steps in the issue summary, but couldn’t reproduce it. If anyone else is experiencing this, please share detailed steps to reproduce, including configuration settings, specific inputs causing the issue, and any error messages or logs. This will help in identifying whether it’s environment-specific or a broader issue.

@divyansh.gupta thanks for trying to test. It seems almost random whether a site is affected so maybe we will never know the answer.