iRule to block multiple user agents.

Do I need to do something special to reference the data group? Right now my testing is blocking all requests.

iRule:

when HTTP_REQUEST {
  if { [class [string tolower [HTTP::header "User-Agent"]] contains user_agent_blacklist ] } {
    log local0. "User_agent [HTTP::header "User-Agent"] is blacklisted. from: [IP::client_addr] "
    drop
    return 
  }
}

Data Group: