Warning or notification when a field is blank

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Hello all,

I would like to ask a question about the fields that need to be filled in by HR when reviewing an employee's goals. Specifically, HR needs to provide the actual value:

This field is not required and we should keep it in that way. Although, we would like to notify the manager that this field was left blank in case the HR did not provide a value.

Does anyone know if this is possible?

Thank you in advance,
Maria

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