Userform Error with Blank RefEdit.

Hi all,

I've got a userform that the user will enter a row into the RefEdit box and click a command button to perform an action. However if someone enters nothing into the RefEdit box and clicks the command button I get an error midway through the macro so that I have to reset.
There's undoubtedly a way to tell it that upon blank click do nothing, but I haven't learnt how to ask it.
Can anyone help?

p.s. Attached is an example of my problem. I'm beginning to think that I might just become a fruit & veg trader as I keep using them for examples lol.