Customer/EventListener/CustomerGroupListener.php
public function onPreDelete(ResourceEventInterface $event)
    {
        $group = $this->getCustomerGroupFromEvent($event);

        if ($group->isDefault()) {
            throw new IllegalOperationException(); // TODO reason message
        }
    }
public function onPreDelete(ResourceEventInterface $event)
    {
        $group = $this->getCustomerGroupFromEvent($event);

        if ($group->isDefault()) {
            throw new IllegalOperationException(); // TODO reason message
        }
    }
public function onPreDelete ( ResourceEventInterface $ event ) { $ group = $ this -> getCustomerGroupFromEvent ( $ event ) ; if ( $ group -> isDefault ( ) ) { throw new IllegalOperationException ( ) ; // TODO reason message } }
Pre delete event handler.

@param ResourceEventInterface $event

@throws IllegalOperationException
Pre delete event handler .