Why doesn't Zabbix return OK?

Question

Windows

Good afternoon!
Configured Zabbix to monitor a specific file for the presence of a "dash" (-) sign in it with a trigger like this Expression:
{%IP-address%:log["C:\Program Files (x86)\path_to_file\error.log"] .str(-)}=1
As soon as errors with lines containing the "dash" sign are written to the file, notifications from Zabbix are received with the PROBLEM mark in the subject line - in fact, normal and correct behavior.
But as soon as I correct all the errors and the file is cleared (file size 0 bytes), then I expect to receive an email with OK in the subject, which, however, does not happen.
Where am I making a mistake?

Answer 1

Example:
{%IP-address%:log["C:\Program Files (x86)\path_to_file\error.log"].str(-)}=1&{%IP-address%:log["C:\Program Files (x86)\path_to_file\error.log"].nodata(180)}=0