how can htmlagilitypack check if nodes exist on webpage?

Using Vb.net and HtmlAgilityPack is there a way to check if the node exists on the webpage before selecting the node ?

While running my program, if the node doesn't exist at all on the page, I am getting a null exception error message.

I don't want to use

If firsttag(0).InnerText IsNot Nothing Then 

as by using this, the program is already trying to get the value of the node.

I would like to scan the webpage first to see if the node exists

Dim firsttag As HtmlAgilityPack.HtmlNodeCollection = docnews.DocumentNode.SelectNodes("//div[(@class='byline')]") 

Is there anything like

if firsttage(0) search does not exist then Continue For Else