If you want to display the fields of Null values, you need to update your Database Table by removing NOT NULL Constraints on the columns you expect NULL Values to be shown. You can refer to this Article for more info =>
Import And Export Data Using Excel File In ASP.NET MVC[
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The community is ready to help if you post some code where you are facing some Errors, even this is not the case, in the future try to post some code snippets with your question.