Replied 8 September 2017, 2:02 pm EST
Spread uses a subset of Excel's formula syntax. Excel's formula syntax does not provide any means for creating a formula result that is equivalent to a blank cell.
DeepakSharma's suggestion of using "" value (empty string) may or may not work depending on you specific scenario. A cell containing "" value (empty string) will in most cases display similar to a cell contain null value (blank cell). However, "" value and null value are two different values and can produce differrent results when used in other formulas.
If you need a formula to produce a null value then there are a couple of other options to consider.
You could define a custom function that returns null (similar to how the built-in function TRUE() returns true). Then you could use the custom function in your formulas.
If your spreadsheet has a cell that will always be blank then you could use that cell in your formulas to produce a null value. To make the formulas more readable, you could create a custom name that references the blank cell and then use the custom name in your formulas.