Build_in_suggest err

Hello everyone,
I done validation for a field (that cannot be manually created error) is shown but after i entering manually to that field i am entering the tab then it goes to another field there it shows the following trace back error,
Traceback (most recent call last):
File “/home/ubuntu/frappe-bench/apps/frappe/frappe/”, line 62, in application
response = frappe.handler.handle()
File “/home/ubuntu/frappe-bench/apps/frappe/frappe/”, line 22, in handle
data = execute_cmd(cmd)
File “/home/ubuntu/frappe-bench/apps/frappe/frappe/”, line 53, in execute_cmd
return, **frappe.form_dict)
File “/home/ubuntu/frappe-bench/apps/frappe/frappe/”, line 939, in call
return fn(*args, **newargs)
File “/home/ubuntu/frappe-bench/apps/frappe/frappe/desk/”, line 52, in search_link
frappe.response[‘results’] = build_for_autosuggest(frappe.response[“values”])
File “/home/ubuntu/frappe-bench/apps/frappe/frappe/desk/”, line 164, in build_for_autosuggest
for r in res:
TypeError: ‘NoneType’ object is not iterable
any idea for this build_for_autosuggest error