system/Router/Router.php
public function get404Override()
	{
		$route = $this->collection->get404Override();

		if (is_string($route))
		{
			$routeArray = explode('::', $route);

			return [
				$routeArray[0], // Controller
				$routeArray[1] ?? 'index',   // Method
			];
		}

		if (is_callable($route))
		{
			return $route;
		}

		return null;
	}
public function get404Override()
	{
		$route = $this->collection->get404Override();

		if (is_string($route))
		{
			$routeArray = explode('::', $route);

			return [
				$routeArray[0], // Controller
				$routeArray[1] ?? 'index',   // Method
			];
		}

		if (is_callable($route))
		{
			return $route;
		}

		return null;
	}
Returns the 404 Override settings from the Collection.
If the override is a string, will split to controller/index array.