Metadata api doesn't work

[pawanchauhan043]

I used the code snippet as described replacing all the values relevant to my account but it throws an error such as _internalLinkedHashmapError.

flutter doctor
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[✓] Flutter (Channel stable, v1.12.13+hotfix.8, on Mac OS X 10.15.3 19D76, locale en-US)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
[✓] Xcode - develop for iOS and macOS (Xcode 11.3.1)
[✓] Android Studio (version 3.6)
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[✓] VS Code (version 1.43.0)
[!] Connected device
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! Doctor found issues in 1 category.