hook_options_list_alter sample fails on 8.1.8

API page: https://api.drupal.org/api/drupal/core%21modules%21options%21options.api...

While trying to use the sample provided on the api page i get the following error:
Error: Call to a member function id() on null in mymodule_options_list_alter()

The field information is stored in $context['fieldDefinition'] object for now.

To get the field name the sample should look the following way.

function hook_options_list_alter(array &$options, array $context) {
  // Check if this is the field we want to change.
  if ($context['fieldDefinition']->getName() == 'field_option') {
    // Change the label of the empty option.
    $options['_none'] = t('== Empty ==');
  }
}

The ->id() function from the existing sample would return bundle / entity_type and the actual fieldname.