Determine XML Node Exists

This is probably simple, but I'm trying to determine if a node exists in an XML document. I thought I found an answer in this post, How to check whether a node exists or not using powershell without getting exception?, but I didn't get it to work. This is my latest attempt.

foreach ($vendor in $xml.Vendors.Vendor| Where-Object  {$_.Type -match "Send"}) {
    $NodeExists = $vendor.SelectSingleNode($vendor.EncKey)
    if ($NodeExists -ne $null) {
        # Do something
    }
    else {
       # something else
    }
   }

Any help would be greatly appreciated.

EDIT: Here is XML from my test file. I need to find out of EncKey exists or note for each vendor.

<?xml version="1.0" encoding="UTF-8"?>
    <!-- Vendors we will send and retreive files from Get-Send means we will get a file and send them a file Send means we will only send them a file-->
    <Vendors>
        <Vendor Type="Get-Send">
            <Name>Vendor1</Name>            
            <RemotePath>/Remote/Path1/</RemotePath>
            <EncKey>pgpenc.key</EncKey>
        </Vendor>
        <Vendor Type="Send">
            <Name>Vendor2</Name>            
            <RemotePath>/Remote/Path2/</RemotePath> 
            <!-- This one has no EncKey -->         
        </Vendor>
    </Vendors>