HTML Agility pack removes break tag close

Question

I am creating an HTML document using HTML agility pack. I load a template file then append content to it. All of this works, but when I view the output file it has removed the closing tag from my <br/> tags to look like this <br>. What is causing this?

Dim doc As New HtmlDocument()
doc.Load(Server.MapPath("Template.htm"))

Dim title As HtmlNode = doc.DocumentNode.SelectSingleNode("//title")

title.InnerHtml = title.InnerHtml & "CEU Classes"
Dim topContent As HtmlAgilityPack.HtmlNode = doc.GetElementbyId("topContent")

topContent.InnerHtml = html.ToString
doc.OptionWriteEmptyNodes = True
doc.Save(outputFileName, Encoding.UTF8)

More info:

It was removing my closing image tags, after I added doc.OptionWriteEmptyNodes = True, it quite doing that.

Update

This is my code as it stands now that removes the closing BR tag

Dim html As String = "Words<br/>more words"
Dim doc As New HtmlDocument()
Dim title As HtmlNode
Dim topContent As HtmlNode

HtmlNode.ElementsFlags("br") = HtmlElementFlag.Empty
doc.Load(Server.MapPath("Template.htm"))

Title = doc.DocumentNode.SelectSingleNode("//title")
title.InnerHtml = title.InnerHtml & "CEU Classes"

topContent = doc.GetElementbyId("topContent")
topContent.InnerHtml = html.ToString

doc.OptionWriteEmptyNodes = True
doc.Save(outputFileName, Encoding.UTF8)

Update 2

I ended up just reading in my template file as a standard string then loading the html like this

Dim TemplateHTML As String = File.ReadAllText(Server.MapPath("Template.htm"))

TemplateHTML = TemplateHTML.Insert(TemplateHTML.IndexOf("<div id=""topContent"">") + "<div id=""topContent"">".Length, _
                                   html.ToString)

doc.LoadHtml(TemplateHTML)

Answer 1

It happens because the Html Agility Pack handles the BR in a special way. It still supports old (but existing on the web today) HTML 3.2 syntax where the BR could be declared without a closing tag at all (browsers also still handle it gracefully by the way...).

To change this default behavior, you need to modify the HtmlNode.ElementFlags property, like this:

Dim doc As New HtmlDocument()
HtmlNode.ElementsFlags("br") = HtmlElementFlag.Empty
doc.LoadHtml("<test>before<br/>after</test>")
doc.OptionWriteEmptyNodes = True   
doc.Save(Console.Out)

which will display:

<test>before<br />after</test>

Answer 2

As per @Simon Mourier, the following C# code works in version 1.4

var doc = new HtmlDocument();
HtmlNode.ElementsFlags["br"] = HtmlElementFlag.Empty;
doc.OptionWriteEmptyNodes = true;
doc.LoadHtml("Lorem ipsum dolor sit<br/>Lorem ipsum dolor sit");

var postParsed = doc.DocumentNode.WriteTo();

has the following string value for postParsed

"Lorem ipsum dolor sit<br />Lorem ipsum dolor sit"