Due to ZBX-6883 there should actually no placeholder necessary anymore, when a function does not need a parameter.

Could be also worth to think about changing foo(0) to foo() for all examples found in the documentation (list may not be complete):

https://www.zabbix.com/documentation/2.4/manual/appendix/triggers/functions
https://www.zabbix.com/documentation/2.4/manual/config/triggers/expression
https://www.zabbix.com/documentation/2.4/manual/config/macros/usermacros
https://www.zabbix.com/documentation/2.4/manual/config/triggers/suffixes
https://www.zabbix.com/documentation/2.4/manual/appendix/macros/supported_by_location
https://www.zabbix.com/documentation/2.4/manual/xml_export_import/hosts
https://www.zabbix.com/documentation/2.4/manual/api/reference/configuration/export
https://www.zabbix.com/documentation/2.4/manual/api/reference/configuration/import
...