fix(webex-core): guard against undefined newMetrics

[Coread]

COMPLETES #< INSERT LINK TO ISSUE >

This pull request addresses

newMetrics is not guaranteed to be defined at this point. This was causing a failure in the token integration test

by making the following changes

< DESCRIBE YOUR CHANGES >

Change Type

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Tooling change
• Internal code refactor

The following scenarios were tested

< ENUMERATE TESTS PERFORMED, WHETHER MANUAL OR AUTOMATED >

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• This PR is related to
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  • Defect fix
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I certified that

• I have read and followed contributing guidelines
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• All existing and new tests passed
• I have updated the documentation accordingly

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