Easy Breadcrumb could not determine the title to use for /node/{node}/translations

Problem/Motivation

The node edit route is created in \Drupal\node\Entity\NodeRouteProvider and has neither a '_title' nor a '_title_callback'.

That was fine until this commit: https://cgit.drupalcode.org/easy_breadcrumb/commit/?id=4d2df56

Before this commit

$title = $this->titleResolver->getTitle($route_request, $route_match->getRouteObject());

resulted in $title being NULL, and therefore !isset($title) being TRUE, and therefore a fallback title was created via

$title = str_replace(array('-', '_'), ' ', Unicode::ucfirst(end($path_elements)));

But after this commit

$title = $this->getTitleString($route_request, $route_match, $replacedTitles);

results in $title being FALSE, and therefore !isset($title) being FALSE, and therefore a no fallback title is created anymore.

Proposed resolution

The function getTitleString should return NULL instead of FALSE.

Remaining tasks

Review.

User interface changes

Breadcrumb for node edit available again.

API changes

None.

Data model changes

None.