GlideRecord - is NULL or does not contain value

I have a situation where I need to query our groups via GlideRecord and I need to check if "type" is either null or does not contain one of the types. I've tried a few different ways of doing this, but either don't return the null types, return all groups, or don't get any groups. This is the current script (returns nothing because of the addnullquery):

//Check group membership

  var m = new GlideRecord('sys_user_grmember');

  m.addQuery('user',current.sys_id);

  m.query();

  var groupList = [];

  while(m.next()){

  groupList.push(m.group + '');

  }

  groupList = new ArrayUtil().unique(groupList);

  var gm = new GlideRecord('sys_user_group');

  gm.addQuery('sys_id','IN',groupList);

  gm.addQuery('type','DOES NOT CONTAIN','64d411974f082240709af7e18110c76c');

  var gm2 = gm.addNullQuery('type');

  gm2.orderBy('name');

  gm2.query();

  while(gm2.next()){

  gs.info('2MonitorInactiveUsers Group' + gm2.name + 'Member');

  addToDescription('Group',gm2.name,'Member');

  }