Plugin strToTime is missing defaultConfiguration()

The tamper plugins are coming from the tamper module, moving the issue over there.

The reason for the error message is that the strToDate plugin has 2 config properties but the defaultConfiguration() method is missing. Therefore, the fallback for both properties is an empty string, which is not a valid default value for a checkbox. If the default values will be added (similar to e.g. \Drupal\tamper\Plugin\Tamper\TruncateText::defaultConfiguration), then the error messages will be gone.

The other error message is a deprecation message from Drupal core which has to be ignored, we can't do anything about that. EDIT: it's not from core, it comes from the entity module, and there is this issue available with a proposed fix: #3532309: Fix Deprecation notice from DeleteAction class causes errors in ECA module

None of the above error messages should prevent the update hook from doing its work, though.

Hm, for this particular plugin, the defaults should be NULL. I think that's why defaultConfiguration() is not defined. The method getSetting() would return NULL if the setting key is not defined.

Is a checkbox field not allowed to have NULL as default? Then it should probably become FALSE if $this->getSetting(static::SETTING_FALLBACK) returns NULL.

Current code for the checkbox field:

$form[static::SETTING_FALLBACK] = [
  '#type' => 'checkbox',
  '#title' => t('Fallback to strtotime() if the date could not be parsed with the provided date format.'),
  '#default_value' => $this->getSetting(static::SETTING_FALLBACK),
  '#states' => [
    'visible' => [
      'input[name="plugin_configuration[date_format]"]' => ['filled' => TRUE],
    ],
  ],
];

(note: I see it is calling t() instead of $this->t().)

But I'm willing to define defaultConfiguration() just with both setting keys set to NULL. Would that help?

I think that NULL is not a valid default for checkboxes, it should indeed be FALSE. And the default for the date format should be an empty string, I'd say.

Those 2 values would also be the settings that you get from \Drupal\tamper\Plugin\Tamper\StrToTime::submitConfigurationForm when the form gets submitted, even if the default values had been NULL.

Do the changes in the MR help to resolve the issue?

LGTM

Thanks, the MR fixes the "Found config field fallback" messages for me, too.

Merging the code is scheduled to be merged. Thanks all for testing!