Overrides Drupal\Core\Entity\EntityFormController::validate().
Overrides EntityFormController::validate
public function validate(array $form, array &$form_state) {
parent::validate($form, $form_state);
// Make sure that the machine name of the vocabulary is not in the
// disallowed list (names that conflict with menu items, such as 'list'
// and 'add').
// During the deletion there is no 'machine_name' key.
if (isset($form_state['values']['machine_name'])) {
// Do not allow machine names to conflict with taxonomy path arguments.
$machine_name = $form_state['values']['machine_name'];
$disallowed = array(
'add',
'list',
);
if (in_array($machine_name, $disallowed)) {
form_set_error('machine_name', t('The machine-readable name cannot be "add" or "list".'));
}
}
}