Q: If you play Trash Something (or Trash a Keeper), can you choose not to trash something?

…For example, if you’re the only one with Keepers, or the only thing on the table is your opponent’s Creeper…can you choose to do nothing?

A: No, you cannot trash nothing. If you play Trash Something and there’s something available to trash, you must discard it. If you play Trash a Keeper, and you’re the only one with Keepers, you must trash one of your own.