Can't Remove Lines From A Canvas Layer

I am creating a custom canvas layer like so:

CanvasLayer.define(function(canvas) {...});

In the body, I add some lines based on current data then call canvas.update(). When the data changes, I need to remove all the lines and add new ones. So, when data has changed I simply loop through the lines and call line.destroy() on each one.

This works if there are a just one or two lines. But when there are lots of lines, canvas.update() throws:

this._canvas is null
http://localhost:49573/oviss/Scripts/telogis.geobase.min.js
Line 1

Telogis code is minfied so I can't tell exactly where the throw happens.

If I do not destroy the old lines, there is no error, but then the old lines hang around.