public function getLastPage(string $group = 'default')
	{
		$this->ensureGroup($group);

		if (! is_numeric($this->groups[$group]['total']) || ! is_numeric($this->groups[$group]['perPage']))
		{
			return null;
		}

		return (int)ceil($this->groups[$group]['total'] / $this->groups[$group]['perPage']);
	}