The Parse Blank operator uses the keyword 'blank' to indicate an empty string value.

when input is⇓ story test fixture check plain test 'sample domain' set name blank check name blank check 'name length' 0 check name Bob set name Bob check name blank sample domain set name blank check name blank check name length 0 check name Bob expected actual Length expected 3 was 0 set name Bob check name blank expected Bob actual Length expected 0 was 3

'sample domain' set name blank check name blank check 'name length' 0 check name Bob set name Bob check name blank

then output is

sample domain set name blank check name blank check name length 0 check name Bob expected actual Length expected 3 was 0 set name Bob check name blank expected Bob actual Length expected 0 was 3