code: func CloneSelectorAndAddLabel(selector *LabelSelector, labelKey, labelValue string) *LabelSelector {
  	if labelKey == "" {
  		// Don't need to add a label.
  		return selector
  	}
  
  	// Clone.
  	newSelector := selector.DeepCopy()
  
  	if newSelector.MatchLabels == nil {
  		newSelector.MatchLabels = make(map[string]string)
  	}
  
  	newSelector.MatchLabels[labelKey] = labelValue
  
  	return newSelector
  }
docs: // Clones the given selector and returns a new selector with the given key and value added.
  // Returns the given selector, if labelKey is empty.