Duplicated person can be added if name is lowercase

[todoge]

UG says no 2 person can have the same name.

To duplicate,
add n/iohn Doe p/98765432 e/johnd@example.com ta/john_doe123
add n/John Doe p/98765432 e/johnd@example.com ta/john_doe123

[nus-pe-bot]

Team's Response

No response provided.

Items for the Tester to Verify

❓ Issue severity

Team chose [severity.Low]
Originally [severity.Medium]

• I disagree

Reason for disagreement: Dev team never gave a reason for downgrading the severity.

The bug is closer to a medium than a low since duplicated persons can be added and it can cause confusion to the user later on.
It is likely to affect the normal operations since users can add a duplicated person accidentally without knowing and this is likely to happen quite often when the user is adding new persons without checking first.

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