Greetings, people of 2009.
I come from the future to say two things:
By the end of 2012, this post will top the Google rankings for 'jQuery "this.empty is not a function"'.
A common cause for this error (probably also the cause in this case) is calling .text on a jQuery object (note no brackets/parenthesis). Either you're calling .text on the wrong thing, and meant to call it on a non-jQuery object (as in this case), or, you actually meant to call the jQuery method, .text() (note the brackets/parenthesis)
It's jQuery that is calling .empty(), not your code.
I will now return to 2012.