code: def update_resolver_nameservers(resolver, nameservers, nameserver_filename):
      
      if nameservers:
          resolver.nameservers = nameservers
      elif nameserver_filename:
          nameservers = get_stripped_file_lines(nameserver_filename)
          resolver.nameservers = nameservers
      else:
          # Use original nameservers
          pass
  
      return resolver
docs: Update a resolver's nameservers. The following priority is taken:
          1. Nameservers list provided as an argument
          2. A filename containing a list of nameservers
          3. The original nameservers associated with the resolver