ExcelImporter: Unique validation rule applied when importing records in which value is empty
I have a use case in which an excelfile is used to enter certain numbers for persons coming from external systems. The number is unique and in the datamodel there is a unique validation rule applied. I would like to initially fill the spreadsheet with all the persons in the system, have an employee fill the spreadsheet with the numbers whenever they come in and regularly import the spreadsheet in the application. The issue that I have now is that when a number has not been entered I get a message that the number already exists. I'd like the system to neglect those. How can I accomplish this?