code: func (t *awsTagging) addFilters(filters []*ec2.Filter) []*ec2.Filter {
  	// if there are no clusterID configured - no filtering by special tag names
  	// should be applied to revert to legacy behaviour.
  	if len(t.ClusterID) == 0 {
  		if len(filters) == 0 {
  			// We can't pass a zero-length Filters to AWS (it's an error)
  			// So if we end up with no filters; just return nil
  			return nil
  		}
  		return filters
  	}
  	// For 1.6, we always recognize the legacy tag, for the 1.5 -> 1.6 upgrade
  	// There are no "or" filters by key, so we look for both the legacy and new key, and then we have to post-filter
  	f := newEc2Filter("tag-key", TagNameKubernetesClusterLegacy, t.clusterTagKey())
  
  	// We can't pass a zero-length Filters to AWS (it's an error)
  	// So if we end up with no filters; we need to return nil
  	filters = append(filters, f)
  	return filters
  }
docs: // Add additional filters, to match on our tags
  // This lets us run multiple k8s clusters in a single EC2 AZ