Unable to Remove Optional Fields of a Company

[RobotWizzard]

The current implementation of the edit command does not allow for setting an optional field (PHONE, ADDRESS) to empty. To remove an optional field, the user would have to delete the company and re-add it without the optional field.

It would be useful for the user to able to remove optional fields in case they entered incorrect data.

Example:

1. Add a company with an optional field (e.g. add n/Google LLC t/FAANG e/contact@google.com p/1234567 t/tech)
2. The user realises that they entered an incorrect phone number but is also unable to find the Google's phone number.
3. The user then tries to edit the company with the edit command and set the PHONE field to empty, but is met with an error: