Value is out of 32-bit integer bounds

A Custom Sensor receives values (0-4) from an SNMP Agent. Sometimes our SNMP Agent is buggy and doesn't send a vlaue. This results in that the next OID is taken as value of the previous OID. The Problem is that the OID is recognized as value "-9223372036854775808", which is an out of 32-bit integer. This happens very rarely,but when it occurs, the custom sensor turns into down state. A custom string sensor could solve this, but the custom string sensor cannot handle multiple values to output different states, or multiple equal states.

As our development doesn't fix the SNMP Agent bug (what would be the best solution), i kindly ask if there is a possibility to bypass such values to bring Sensor not in down state when a non 32-bit integer is received. In the Lookup File i can only define "undefined values" but this doesn't solve the issue.