C# - getting a specific node type from Group

Hey there,
Coming to Godot from Unity. I'm wondering how I would go about getting a specific type, like NavMesh, from an object added to a group - I don't really see why this code wouldn't work. If possible I'd prefer to avoid querying parents and such to find the component

Node navMeshObject = GetTree().GetNodesInGroup("NavigationMesh")[0];
navMesh = (NavigationMesh)navMeshObject;