Cannot send test email

This commit https://github.com/cividesk/com.cividesk.email.sparkpost/commit/85a4a89162b2c5f273c95503da6902d7e49499ad breaks sending test emails for me. I didn't test whether it also breaks sending other email but I'm guessing it does.

When pressing "Save and Send Test Email" from: Administer->System Settings->Outbound Email (Sparkpost)

I get the following error:

Sending test email. FROM: XXX@XXX TO: YYY@YYY.
Oops. Your SparkPost settings are incorrect. No test mail has been sent.
An error occurred when CiviCRM attempted to send an email (via SMTP). If you received this error after submitting on online contribution or event registration - the transaction was completed, but we were unable to send the email receipt.

The mail library returned the following error message:
Sparkpost error: HTTP return code 405, Sparkpost error code 1102 (invalid http method: PUT is not supported on /api/v1/transmissions). Check https://support.sparkpost.com/customer/en/portal/articles/2140916-extended-error-codes for interpretation.

This is probably related to a problem in your Outbound Email Settings (Administer CiviCRM » System Settings » Outbound Email), OR the FROM email address specifically configured for your contribution page or event. Possible causes are:

Your Sendmail path is incorrect.
Your Sendmail argument is incorrect.
The FROM Email Address configured for this feature may not be a valid sender based on your email service provider rules.