Blank test?

Angel • Baby Number #1 08.Dec.2018👶🏼🌈❤️🇬🇧 Due March 2020💗💙

So I took a Superdrug digital test, it’s blank? Normally the show up with a + or a - (obviously) I’ve waited 10 minutes and nothing is happening, I’ve lost the box so I don’t know what happens?! Does this mean it’s invalid orrrr