If the only experience you have is several years spent writing derivative fiction, is it better to write nothing under your bio and leave it out completely, or is derivative fiction an acceptable medium of experience, particularly if the fandom which you had written for has since generated a handful of best sellers?
All of us started with no credits or experience. I can finesse the question "what have you sold" about seventeen different ways cause the first year of my agenting career I hadn't sold much at all. That said, I often found the most persuasive thing to say was "I haven't sold much; I don't have a big client list; you'll get a lot of attention" and oddly enough, writers with me to this day said "ok."
I mention this because writing credits (unlike agent's sales) don't really mean much. There are exceptions: if you write lit fic and you've had stories pubbed in the big periodicals like the New Yorker, yes, that helps.
I'd rather you SHOW me you can write well, rather than tell me where you learned how to do it, which is what writing fan fiction is in my opinion. Like the great genre writers of old (John D. MacDonald, Erle Stanley Gardner etc) who cut their teeth writing for the pulps, a lot of writers we'll soon be admiring are learning how to write on the fan fic sites.
Bottom line: until you've got an well-stocked CV, it's ok to just say "this is my first novel" and let me find out you're an amazing writer when I read it.