Allow adding duplicated email address for `add` command

[choowengyan]

As shown in the screenshot below, the program allow user to insert duplicated email address for different person (Client index 12 and 13).

In real-world scenario, email address should be unique, and no more than one person can have the same email address. In this case, it will cause the user to send information to the wrong person as the email address entered are duplicated and caused inconvenience to the user to double check the accuracy of insertion.

It would be great for the team to detect duplication in the insertion of email address such that duplicated email address is not allowed/ warning message can be shown.

[nus-se-bot]

Team's Response

In our documentation, we stated the following:

We downgraded the severity to low, as this scenario only happens rarely (people do not edit their client's emails to be duplicates of other client's emails often, if not at all).

This case also qualifies for the highlighted case, as duplicate detection based on email is currently not a feature, although it has been identified as a planned enhancement, and trying to use the missing feature does not cause the software to crash.

Items for the Tester to Verify

:question: Issue response

Team chose [response.NotInScope]

• [ ] I disagree

Reason for disagreement: [replace this with your explanation]

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## :question: Issue severity Team chose [`severity.Low`] Originally [`severity.Medium`] - [ ] I disagree **Reason for disagreement:** [replace this with your explanation]

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