If you create an empty `L.Polyline` without adding to the map, add latlngs then then try to add to the map `this._bounds` is an empty `L.LatLngBounds` object. Therefore `this._bounds.getNorthWest()` will error.

This is because `L.Path.redraw` doesn't call `L.Renderer._update` since `this._map` doesn't exist (as it hasn't been added to the map yet).

E.g.

````js
var a = L.polyline([]);
a.addLatLng([[0,0],[1,1],[1,2]);
map.addLayer(a);
````