title: Unused Service Templates can’t be deleted
body: <p>I made a mistake and I only wanted to delete the Service Template. I clicked on the template and then on modify to delete this. Then I got an Error:</p>
  <blockquote>
  <p>Uncaught Error: Call to a member function toString() on null in
  /usr/share/icingaweb2/modules/director/application/controllers/ServiceController.php:250
  Stack trace:
  #0 /usr/share/icingaweb2/modules/director/library/Director/Web/Controller/ObjectController.php(465):
  Icinga\Module\Director\Controllers\ServiceController-&gt;loadObject()
  #1 /usr/share/icingaweb2/modules/director/library/Director/Web/Controller/ObjectController.php(89):
  Icinga\Module\Director\Web\Controller\ObjectController-&gt;loadOptionalObject()
  #2 /usr/share/icingaweb2/modules/director/application/controllers/ServiceController.php(41):
  Icinga\Module\Director\Web\Controller\ObjectController-&gt;init()
  #3 /usr/share/php/Icinga/Web/Controller/ActionController.php(152): Icinga\Module\Director\Controllers\ServiceController-&gt;init()
  #4 /usr/share/php/Icinga/Web/Controller/Dispatcher.php(59): Icinga\Web\Controller\ActionController-&gt;__construct(Object(Icinga\Web\Request),
  Object(Icinga\Web\Response), Array)
  #5 /usr/share/icingaweb2/library/vendor/Zend/Controll</p>
  <p>#0 [internal function]: Icinga\Application\Web-&gt;Icinga\Application{closure}()
  #1 {main}</p>
  </blockquote>
  <ul>
  <li><p>Icinga Web 2 version: 2.6.2</p>
  </li>
  <li><p>Used modules and their versions:
  |director|master|
  |incubator|0.6.0|
  |ipl|v0.5.0|
  |monitoring|2.6.2|
  |reactbundle|0.8.0|</p>
  </li>
  <li><p>Web browser used: Google Chrome</p>
  </li>
  <li><p>Icinga 2 version used (icinga2 --version): version: r2.10.3-1</p>
  </li>
  <li><p>PHP version used (php --version): PHP 7.3.29-1~deb10u1 (cli)</p>
  </li>
  <li><p>Server operating system and version: Debian GNU/ LINUX 10 (buster)</p>
  </li>
  </ul>