Unable to clear session token from Azure DevOps AWS Service Connection

[xyfoo]

Describe the bug

Unable to clear out session token from Azure DevOps's service connection, if it was previously assigned. I have to delete and recreate the service connection to get around this issue.

To reproduce

1. Create a new service connection, and enter a valid access key id & secret access key
2. Run pipeline with AWS task, which will run successfully
3. Edit the service connection, enter an invalid session token
4. Rerun same pipeline, which will fail as expected
5. Edit the service connection, reenter the valid access key id & secret access key, and clear the session token field.
6. Rerun pipeline, failed with the error message: An error occurred (UnrecognizedClientException) when calling the GetAuthorizationToken operation: The security token included in the request is invalid

Expected behavior

The 3rd attempt to run should success, with only the access key id & secret key passed on to aws task

Screenshots

Your Environment

• On-prem or cloud based? Cloud
• Azure DevOps version:
• AWS Toolkit for Azure DevOps version: 1.13.0

Additional context

• Tested using an IAM account's credential without key rotation

[captrespect]

OMG. This cost me a few hours yesterday and today. I couldn't figure why I was getting authentication errors. Please fix this.