code: func (n *NodeLabelChecker) CheckNodeLabelPresence(pod *v1.Pod, meta PredicateMetadata, nodeInfo *schedulernodeinfo.NodeInfo) (bool, []PredicateFailureReason, error) {
  	node := nodeInfo.Node()
  	if node == nil {
  		return false, nil, fmt.Errorf("node not found")
  	}
  
  	var exists bool
  	nodeLabels := labels.Set(node.Labels)
  	for _, label := range n.labels {
  		exists = nodeLabels.Has(label)
  		if (exists && !n.presence) || (!exists && n.presence) {
  			return false, []PredicateFailureReason{ErrNodeLabelPresenceViolated}, nil
  		}
  	}
  	return true, nil, nil
  }
docs: // CheckNodeLabelPresence checks whether all of the specified labels exists on a node or not, regardless of their value
  // If "presence" is false, then returns false if any of the requested labels matches any of the node's labels,
  // otherwise returns true.
  // If "presence" is true, then returns false if any of the requested labels does not match any of the node's labels,
  // otherwise returns true.
  //
  // Consider the cases where the nodes are placed in regions/zones/racks and these are identified by labels
  // In some cases, it is required that only nodes that are part of ANY of the defined regions/zones/racks be selected
  //
  // Alternately, eliminating nodes that have a certain label, regardless of value, is also useful
  // A node may have a label with "retiring" as key and the date as the value
  // and it may be desirable to avoid scheduling new pods on this node