I'm trying to validate data using an excel sheet which contains data validations. e.g. I've created list data validation on column named category which allows values (X, Y, Z and " "). But I've observed that because of the blank value in the source list, it allow any invalid values ( A,B). My intention to add a blank value in the source list is to allow a blank value only. But it violates my purpose. Is it the correct behaviour or should it only allow values which are there in the source list (including blank value)?