ExportAuthCert.ps1 fails because Auth Certificate is not exporting on line 7 on Exchange 2013 CU21

I'm trying to follow the steps listed here and getting stuck on step 3 while running ExportAuthCert.ps1:

$thumbprint = (Get-AuthConfig).CurrentCertificateThumbprint  
if((test-path $env:SYSTEMDRIVE\OAuthConfig) -eq $false)  
{  
   md $env:SYSTEMDRIVE\OAuthConfig  
}  
cd $env:SYSTEMDRIVE\OAuthConfig  
$oAuthCert = (dir Cert:\LocalMachine\My) | where {$_.Thumbprint -match $thumbprint}  
$certType = [System.Security.Cryptography.X509Certificates.X509ContentType]::Cert  
$certBytes = $oAuthCert.Export($certType)  
$CertFile = "$env:SYSTEMDRIVE\OAuthConfig\OAuthCert.cer"  
[System.IO.File]::WriteAllBytes($CertFile, $certBytes)  

If I look at the value of $oAuthCert after line 7, it returns nothing. Line 8 doesn't throw an error, but line 9 does when it tries to export $oAuthCert to a file (since it is null).

You cannot call a method on a null-valued expression.
At C:\users\jdale\desktop\ExportAuthCert.ps1:9 char:1

• $certBytes = $oAuthCert.Export($certType)
• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• CategoryInfo : InvalidOperation: (:) [], RuntimeException
• FullyQualifiedErrorId : InvokeMethodOnNull

Exception calling "WriteAllBytes" with "2" argument(s): "Value cannot be null.
Parameter name: bytes"
At C:\users\jdale\desktop\ExportAuthCert.ps1:11 char:1

• [System.IO.File]::WriteAllBytes($CertFile, $certBytes)
• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• CategoryInfo : NotSpecified: (:) [], MethodInvocationException
• FullyQualifiedErrorId : ArgumentNullException

When I look through the certificate store, I do not find any certificate matching the thumbprint that was returned on the first line. There must be some way to update that thumbprint, anyone know how?