Sematics of NETSNMPTRAPD_HANDLER_{OK,FAIL} in NetSNMP::TrapReceiver

Hello.

I've written a Perl plugin for snmptrapd that sends Host/Service check results to Nagios/Icinga monitoring without the need for snmptt.
It all works, but I'm unsure about the exact semantics of the return codes NETSNMPTRAPD_HANDLER_FAIL vs. NETSNMPTRAPD_HANDLER_OK in my receiver registered via NetSNMP::Trapreceiver::register().
If I fail to extract the TrapOID from the PDU, that's _FAIL.
If I handle the trap and send a command via the monitoring command pipe, that's _OK.
But what am I supposed to return in case everything is OK, my configuration just tells me not to do anything for this combination of Trap OID/variable binds/receivedfrom etc.?

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