I agree, it is a bit messy.
If I was trying to do an if statement where the only requirement was that the field 'is not blank' then, for an email address field for example, I would select the if email address and then choose 'is not empty' rather than 'if not' from the drop down list. But I'm not sure how you can combine that with 'not google' in the same if statement....
If you didn't want anyone with a blank value to be affected by your other choice statements you could maybe try something like this:
choice 1 -if search engine is empty do nothing/ do -x- (so having this as choiuce 1 would mean leads with a blank value are not affected by any other choices 2,3,...)
choice 2-if search engine is google do y
choice 3-if search engine is not google do z (or whatever your other choices are !)
This is only an idea though, it's not a solution I've tested myself...
I will keep having a think about it though and get back to you if I come up with something else that is a bit more efficient than the first suggestion 🙂