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: helpers.go
    path of file: ./repos/devspace/vendor/k8s.io/apimachinery/pkg/apis/meta/v1
    
    the code of the file until where you have to start completion: /*
Copyright 2016 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or impli
    
func LabelSelectorAsMap(ps *LabelSelector) (map[string]string, error) {
	if ps == nil {
		return nil, nil
	}
	selector := map[string]string{}
	for k, v := range ps.MatchLabels {
		selector[k] = v
	}
	for _, expr := range ps.MatchExpressions {
		switch expr.Operator {
		case LabelSelectorOpIn:
			if len(expr.Values) != 1 {
				return selector, fmt.Errorf("operator %q without a single value cannot be converted into the old label selector format", expr.Operator)
			}
			// Should we do anything in case this will override a previous key-value pair?
			selector[expr.Key] = expr.Values[0]
		case LabelSelectorOpNotIn, LabelSelectorOpExists, LabelSelectorOpDoesNotExist:
			return selector, fmt.Errorf("operator %q cannot be converted into the old label selector format", expr.Operator)
		default:
			return selector, fmt.Errorf("%q is not a valid selector operator", expr.Operator)
		}
	}
	return selector, nil
}