[Bug] Return 0 when hex(0)

[EmmyMiao87]

Proposed changes

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• Bugfix (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 not work as expected)
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Checklist

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• I have created an issue on (Fix #ISSUE) and described the bug/feature there in detail
• Compiling and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
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Further comments

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[morningman]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[zbtzbtzbt]

LGTM, this is my negligent bug.