There are certain SNMP devices, that can return incorrectly formatted data:

Wrong Type (should be Counter64): Hex-STRING: 00 00 1D B0 EF AF 8B 67

But Zabbix interprets this as an empty result. although it contains the actual HEX value that's needed:

It's impossible to use the value with any type of preprocessing, because Zabbix gets an empty string.

 Zabbix should be able to use the value that is there instead of just returning empty value.