Singular query scope returning empty array when nothing found

I am trying to create a query scope which returns the first latest or null.

I created it like this:

public function scopeUpcomingAction()
{
    $upcomingAction = $this->actions()->latest()->whereNotNull('completed_at')->take(1);
    if ($upcomingAction->exists()) {
        return $upcomingAction;
    } else {
        return null;
    }
}

However when I use this scope like this:

    return $subject->load([
        'tasks' => function($query) {
            $query->with('upcomingAction');
        }
    ]);

when upcomingAction is null it gives me an empty array like this:

    {
        "id": 3,
        "created_at": "2018-01-13 19:08:30",
        "updated_at": "2018-01-13 19:08:30",
        "upcoming_action": []
    }

Can this be told to be singular?