We didn't have any arrangements either, the only plan we had was that we'd probably get married in May (in the end we got married in June...).
If you had to get married within a month I could understand the ECO insisting that you had some sort of idea, but you have up to 6 months to arrange a wedding which is plenty long enough. I'd also argue that a couple ought to plan a wedding together, and you can't do that until you are both in the country in which you plan to get married.
