Unsupported operand types error when creating new Webform handler

Question

Following the example here: https://www.drupal.org/docs/8/modules/webform/webform-cookbook/how-to-programmatically-add-a-handler-to-a-new-webform

I've created my handler manager sucessfully, however, when I go to create the handler, I get the error

Error: Unsupported operand types in Drupal\webform\Plugin\WebformHandlerBase->setConfiguration() (line 363 of /var/www/sitename/web/modules/contrib/webform/src/Plugin/WebformHandlerBase.php

Here's a sample of the code I'm using to get this error

$webform_machine_name = 'form_id';
$webform = \Drupal\webform\Entity\Webform::load($webform_machine_name);

$handler_manager = \Drupal::service('plugin.manager.webform.handler');

// Create webform handler.
$handler_configuration = [
  'id' => 'my_form_handler',
  'label' => 'My form handler',
  'handler_id' => 'my_form_handler',
  'status' => 1,
  'weight' => 0,
  'settings' => [],
];

$handler = $handler_manager->createInstance('my_form_handler', $handler_configuration );

Answer 1

When I look at line 263 in \Drupal\webform\Plugin\WebformHandlerBase there is the below code...

$this->configuration = $configuration['settings'] + $this->defaultConfiguration();

Your Unsupported operand types error message indicates that one of those variables/properties is not an array.

My best guess is that \Drupal\webform\Plugin\WebformHandlerBase::defaultConfiguration is not returning an array() because your $configuration['settings'] is set to an empty array.