irule to drop null dns queries

Greetings!!!

I was curious if anyone else has had to deal with TONS of null queries to their external dns and if you had any luck dropping those? I am trying to get it to do it via an irule but not having much luck. I have checked out lots of different articles but cant seem to get it quite right.

I have tried:

when DNS_REQUEST{

if { [DNS::question type] equals "null" } {

DNS::drop

}

}

#and this

when DNS_REQUEST {

if {[DNS::question type] equals "10"} {

DNS::drop

}

}

# we also tried using empty rrname

when DNS_REQUEST {

if { [DNS::rrname] equals "" } { <-- this gave an error

DNS::drop

}

}

Any ideas on a way to block these effectively? We are running 14.1, and have a ticket open with support. Will post back if they see where we missed it.