Unsubscribe command does not work as intended

[nus-se-bot]

Describe the bug A clear and concise description of what the bug is. The unsubscribe command does not work To Reproduce Steps to reproduce the behavior:

1. Open the jar file
2. Type unsubscribe
3. See error

Expected behavior Expected to see a success message of some sort but shows unknown command

Screenshots

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Reported by: @jing1324 Severity: High

_{[original: nus-cs2103-AY1819S2/pe-dry-run#156]}

[qjqqyy]

context?

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