Zowe config secure fails if no creds entered for apiml

[adam-wolfe]

Describe the bug

In testing with 8.26.1 and 8.26.2, if I have a profile that goes through the mediation layer, when I run zowe config secure, the command will fail if I enter nothing for the API ML creds.

Expected and actual results
I would expect to be able to enter nothing and continue entering secure values for other properties.

8.26.1 or 8.26.2:

This does not happen with 8.21.0:

Describe your environment

• Zowe CLI version installed (run command zowe --version): 8.26.1 and 8.26.2
• Shell/terminal (bash, cmd, powershell, etc...): Powershell
• Daemon mode enabled or disabled: Disabled

Additional context

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