If you try to create a trigger prototype without an item prototype, you will see the following message:

Created: Trigger prototype "trigger" on "trapper-host 2".
Trigger "trigger:

=0" does not have item prototype. [trigger_prototypes.php:166 ? CAPIObject->create() ? CAPIObject->__call() ? czbxrpc::call() ? czbxrpc::callAPI() ? call_user_func() ? CTriggerPrototype->create() ? CZBXAPI::exception() in /opt/lampp/htdocs/zabbix/trunk/frontends/php/api/classes/CTriggerPrototype.php:523]

There are several problems with it:
1. It says that the prototype was created, even when it wasn't.
2. The expression in the error message is imploded.
3. The error message is grammatically incorrect. It should be changed to something like "Trigger prototype expression %expression% must contain at least one item prototype."