code: func Process(labels labels.Labels, cfgs ...*Config) labels.Labels {
  	for _, cfg := range cfgs {
  		labels = relabel(labels, cfg)
  		if labels == nil {
  			return nil
  		}
  	}
  	return labels
  }
docs: // Process returns a relabeled copy of the given label set. The relabel configurations
  // are applied in order of input.
  // If a label set is dropped, nil is returned.
  // May return the input labelSet modified.