TYPO3 Extbase: Assigning 2 different objects to the view? - typo3

Question

I have a showAction in my Controller of the class "Termin" that not only assigns the object of that class to the view, but it should also pass a second object that is in relation to that object via the getter.
public function showAction(\...\Kundentermine\Domain\Model\Termin $termin)
{
$this->view->assign('termin', $termin);
$this->view->assign('kaufmnnisch', $termin->getZugewkaufmaennisch());
}
The corresponding template should not only show details for the "Termin" object, but also have a link to the show action of another Controller which i pass the second assigned object "kaufmnnisch" to.
<tr>
<td>
<f:link.action action="show" controller="Kaufmnnisch" arguments="{kaufmnnisch : kaufmnnisch}">
<f:translate key="tx_kundentermine_domain_model_termin.kaufmaennisch" />
</f:link.action>
{termin.kaufmaennisch}
</td>
<td>
</td>
</tr>
But i get an error:
Argument 1 passed to ...\Kundentermine\Controller\KaufmnnischController::showAction() must be an instance of ...\Kundentermine\Domain\Model\Kaufmnnisch, null given
Why is the object NULL? Testing "$termin->getZugewkaufmaennisch()" inside a va_dump() within the TerminController gets me the correct object, so why isn't the object assigned to the view?
Edit: As requested, here is the show Action of the Controller "Kaufmnnisch" that gets the object $kaufmnnisch, which supposedly is NULL on arrival, so to speak.
/**
* action show
*
* #param \...\Kundentermine\Domain\Model\Kaufmnnisch $kaufmnnisch
* #return void
*/
public function showAction(\...\Kundentermine\Domain\Model\Kaufmnnisch $kaufmnnisch)
{
$this->view->assign('kaufmnnisch', $kaufmnnisch);
}
Edit2: Problem solved...
The problem was that the object was assigned to the template, but from there it should have been passed to a partial as an argument. So it never arrived ath the point:
<tr>
<td>
<f:link.action action="show" controller="Kaufmnnisch" arguments="{kaufmnnisch : kaufmnnisch}">
<f:translate key="tx_kundentermine_domain_model_termin.kaufmaennisch" />
</f:link.action>
{termin.kaufmaennisch}
</td>
<td>
</td>
</tr>
Now, after i added it here:
<f:render partial="Termin/Properties" arguments="{termin:termin, kaufmnnisch:kaufmnnisch}" />
It works flawlessly.