Nonfiction Or Non-fiction (with a hyphen)

I want my query letter to be perfect, and I'm sure that I'm being picky here, but I see agent websites that use a hyphen, as in "non-fiction." In the "Deals" section on Publishers Marketplace, they use a hyphen for the category (Non-fiction), but no hyphen when describing the deal (nonfiction).

Is using a hyphen the correct way, and is an agent going to care whether or not the writer knows that it is supposed to have a hyphen?

Nonfiction is what I have been using in my query letters. The agent websites have me thinking that I should use non-fiction. Of course, I often see agent websites in which they end their sentences with a preposition.