Bug in PowerShell v5 version of 2016 TP3

TestBug.psm1

# Get-DscResource -Module TestBug | Select-Object -ExpandProperty Properties
# Un-comment the ValidateNotNullEmpty attribute to repro the bug

enum Ensure
{
    Present
    Absent
}

[DscResource()]
class TestBug 
{

    [DscProperty(Key)]
    #[ValidateNotNullOrEmpty()]
    [System.String]
    $DriveLetter

    [DscProperty(Mandatory)]
    [System.String]
    $Path

    [DscProperty(Mandatory)]
    [Ensure]
    $Ensure

    [void] Set()
    {
    }

    [bool] Test ()
    {
        return $true
    }

    [TestBug] Get()
    {
        return $this
    }
}