You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: priority_queue.go
    path of file: ./repos/protoactor-go/actor
    
    the code of the file until where you have to start completion: package actor

// A priority queue is a sort of meta-queue that uses a queue per priority level.
// The underlying queues can be anything that implements the
    
func (q *priorityQueue) Pop() interface{} {
	for p := priorityLevels - 1; p >= 0; p-- {
		if item := q.priorityQueues[p].Pop(); item != nil {
			return item
		}
	}
	return nil
}