I've been told this message is showing up on my company's web site. And it is... in Internet Explorer, in some applications, the yellow-triangle warning appears with this message. But not in Firefox. The code referenced in the message is this code:
This code is using jQuery, and the message 'null' is null or not an object points at Line 9, Char 2. (If that's worth anything.) Which would be this line:
So can anybody tell me what I should be looking for which is making something null in that code?
So I turned on Firebug and debugged that line and...
Several years ago when we wrote those web applications, we used Prototype for our AJAX processing. Then the outside company did the redesign, and they used jQuery for some UI features. So now the page contains both jQuery and Prototype. The first thing I saw when debugging was that $('.extended') called a Prototype script. Obviously this is a Bad Thing.
However almost everything in that script refers to CSS classes which don't actually exist in our pages. At any rate having it crash on the first line doesn't affect the page's behaviour in any way. So it looks like the best thing is just to remove it (and jQuery) from the page entirely.