Exchange 2013 Remove-MailboxExportRequest error: Cannot process argument 'identity'

I have exported several mailboxes from Exchange 2013 to a PST file. Now I want to remove the export requests, since they have completed successfully. I tried 

get-mailboxexportrequest | remove-mailboxexportrequest

and I get the following error:

Cannot process argument transformation on parameter 'Identity'. Cannot convert value "00000000-0000-0000-0000-000000000000" to type
"Microsoft.Exchange.Management.RecipientTasks.MailboxExportRequestIdParameter". Error: "This IdParameter cannot find an object of the specified type.
Parameter name: identity"
    + CategoryInfo          : InvalidData: (uiu.uiu.edu/UIU-Users/UIU-Staff/WalkerA\:PSObject) [Remove-MailboxExportRequest], ParameterBindin...mationException
    + FullyQualifiedErrorId : ParameterArgumentTransformationError,Remove-MailboxExportRequest
    + PSComputerName        : servername.domain.edu

So I run 

Get-mailboxexportrequest

And I see that the name and Identity of the moves are empty, completely.

Using remove-mailboxexportrequest alias\mailboxexport0 doesn't work either.

Using remove-mailboxexportrequest with the requestGUID parameters doesn't work either.

How can I remove this request?

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Kevin