fix: signature should be an empty string by default
fix: signature should be an empty string by default

(would become undefined if the server message was empty)

frappe/frappe,saurabh6790/frappe,saurabh6790/frappe,yashodhank/frappe,mhbu50/frappe,frappe/frappe,almeidapaulopt/frappe,almeidapaulopt/frappe,yashodhank/frappe,mhbu50/frappe,frappe/frappe,yashodhank/frappe,mhbu50/frappe,yashodhank/frappe,saurabh6790/frappe,mhbu50/frappe,StrellaGroup/frappe,StrellaGroup/frappe,saurabh6790/frappe,almeidapaulopt/frappe,almeidapaulopt/frappe,StrellaGroup/frappe