NameValueCollection to IEnumerable, ILookup

NameValueCollectionToLookup.cs

// https://stackoverflow.com/questions/391023/make-namevaluecollection-accessible-to-linq-query

using System;
using System.Collections.Specialized;
using System.Linq;

namespace System.Collections.Specialized
{
    public static class Extensions
    {
        public static ILookup<string, string> ToLookup(this NameValueCollection @this)
        {
            if (@this == null) throw new ArgumentNullException(nameof(@this));

            return @this
                .Cast<string>()
                .SelectMany(key => @this.GetValues(key), (key, value) => new { key, value })
                .ToLookup(p => p.key, p => p.value);
        }
    }
}