Why does Unbrowse have multiple varbindings on simple v1 SNMP packets for a mibwalk? (and why is the value of each varbinding null?)

I thought an SNMP mib walk on V1 consisted of simple get-next requests with no var-bindings and that var-bindings were only to be attached to getbulk (v2c) responses and set-requests?

Thanks,

I'd like to know the exact answer too if possible. Knowing nothing annoys me, meh.