TShirt "" //nothing between the quote marks Red TShirt " " //spaces between the quote marks Price 10.99Null values will not work in Float, Int and DateType fields because of type checking, but they are accepted by Text fields. However, this may cause more confusion than it is worth. For example, your users may not know how many spaces have been used, and queries using NOT will still see the field as containing something.
The situation is even more confusing if vectors are involved:
?Dog Breed_and_weight Text Float Dog: Bowser Age_and_weight "" 80.5If you are tempted to use null values in this way, try redesigning the model instead.