The behavior of the discovery rule (when using the walk[] key) changed some time ago (maybe since 7.4.2 version).
Now the discovery rule reports the error "No Such Object available on this agent at this OID" (if a dynamic snmp table is used and it's empty). However, previously discovered elements aren't deleted.

For example, the snmp table contains a list of connected sensors. If no sensors are connected, it reports the requested OID as missing.

Discovery rule doesn't provide a preprocessing validation option to check for unsupported values ​​(for specify the value manually when got error).

If "snmpwalk to json" is specified first in preprocessing, the discovery rule will not pass further actions to preprocessing when this error occurs.

Expected: discovery rule + snmpwalk to json return "[]" when no oid's