BehaviorInvokerInterface::processEntity() should not throw plugin exceptions

Problem/Motivation

\Drupal\rabbit_hole\BehaviorInvokerInterface::processEntity() describes that the following exceptions were thrown:

@throws \Drupal\Component\Plugin\Exception\PluginException
@throws \Drupal\Component\Plugin\Exception\PluginNotFoundException

It doesn't make sense, as it should be handled in ::getBehaviorPlugin() plugin. If plugin is not available, then method should return NULL.