An empty envelope

Yesterday I got a letter from Midnattsloppet (www.midnattsloppet.com). Or, to be precise, I got an envelope from Midnattsloppet. The envelope was empty. Empty envelopes bring funny thoughts - did they forget all letters? Will they send a new letter, saying how sorry they are for the empty envelope but forget the original message. These thoughts are probably more amusing than the real message but until I get response from Midnattsloppet, I can at least keep fantasizing.