IS NULL operator in Search Builder leads to Catch 22

Accidentally imported a thousand or so organizations with no name. Thought I could easily use Search Builder to find and remove them, but:
1. Searching for Organization -> Display Name -> IS NULL returns an error "Please enter the value."
2. Entering a value in the box, such as "1" or "TRUE" returns an error "Please clear your value if you want to use IS NULL operator."