Fix error when printing environment verification message

[sryze]

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• Tests for the changes are included.

What is the current behavior?

ns doctor android prints an error:

Cannot read property 'toLowerCase' of null

It fails because null is passed as platform to PlatformEnvironmentRequirements.getEnvVerificationMessage().

What is the new behavior?

No error

Fixes/Implements/Closes #[Issue Number].

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