Steps to reproduce:

1. Configure SNMP agent item with walk[1.3.6.1.2.1.47.1.1.1.1.1]
2. Configure preprocessing with "SNMP walk to JSON"
3. Apply to device that currently has no entities connected

Result:
SNMP agent of device returns "No Such Object available on this agent at this OID",
SNMP agent item return "<empty string>"
SNMP walk to JSON preprocessing returns error "no data was found"

Expected:
No error and [] returned just like with discovery[1.3.6.1.2.1.47.1.1.1.1.1].

The table is empty now but I need to monitor it because entities will appear if connected.

Can "SNMP walk to JSON" change so it gives [] for <empty string>?