Purging cache definitions that require identifiers does no work.

To reproduce:

1. Log in as an admin.
2. Browse to Settings > Plugins > Caches > Configuration.
3. Locate the database meta definition in the definitions table.
4. Click Purge under its action links.

Coding error detected, it must be fixed by a programmer: Identifier required for cache has not been provided: dbfamily

More information about this error

Debug info:
Error code: codingerror
Stack trace:
line 760 of /cache/classes/definition.php: coding_exception thrown
line 261 of /cache/classes/loaders.php: call to cache_definition->set_identifiers()
line 178 of /cache/classes/factory.php: call to cache->set_identifiers()
line 169 of /cache/classes/loaders.php: call to cache_factory->create_cache_from_definition()
line 293 of /cache/classes/helper.php: call to cache::make()
line 212 of /cache/admin.php: call to cache_helper::purge_by_definition()