Remove segments where source is duplicated from TMX file while streaming it

NoDuplicatedSource.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml;
using System.Xml.Linq;

namespace DuplicatesInTMX
{
    class Program
    {
        static XElement ReadHeader(XmlReader reader)
        {
            if (reader == null)
                throw new ArgumentNullException("reader");

            reader.MoveToContent();

            while (reader.Read())
            {
                if (reader.NodeType == XmlNodeType.Element
                    && reader.Name == "header")
                {
                    var header = XElement.ReadFrom(reader) as XElement;
                    return header;
                }
            }

            return null;
        }
        static IEnumerable<XElement> NoDuplicatedSource(XmlReader reader)
        {
            if (reader == null)
                throw new ArgumentNullException("reader");

            var duplicates = new Dictionary<string, bool>();
            while (reader.Read())
            {
                if (reader.NodeType == XmlNodeType.Element
                    && reader.Name == "tu")
                {
                    var tu = XElement.ReadFrom(reader) as XElement;
                    var tuv = tu.Element("tuv");
                    if (tuv == null)
                        continue;

                    var source = tuv.Element("seg");
                    if (source == null)
                        continue;

                    var sourceText = source.ToString();
                    if (duplicates.ContainsKey(sourceText))
                        continue;

                    duplicates.Add(sourceText, true);
                    yield return tu;
                }
            }
        }

        static void Main(string[] args)
        {
            if (!args.Any())
            {
                Console.WriteLine("You need to specify a path to TMX file!");
                return;
            }

            XmlReaderSettings settings = new XmlReaderSettings()
            {
                DtdProcessing = DtdProcessing.Ignore
            };

            using (XmlReader reader = XmlReader.Create(args[0], settings))
            {
                var version = new XAttribute("version", "1.4");
                var root = new XStreamingElement("tmx");
                root.Add(version);

                var header = ReadHeader(reader);
                if (header == null)
                    throw new NullReferenceException("There's no header in the file!");

                root.Add(header);

                var body = new XStreamingElement("body",
                    from el in NoDuplicatedSource(reader)
                    select el);

                root.Add(body);
                root.Save("output.tmx");
            }
        }
    }
}