I searched for the posts regarding zeroes vs null values but don't think I found an answer to my question.

So in module A, when people create projects they input values. These values are brought to module C as reporting values.

In module B, people have the ability to upload values from Excel. The formula in module C says , if values uploaded from module B is zero, use the values from module A, otherwise use the uploaded values from module B. So here I don't know how I can create a formula that recognize whether it's a zero from module B (truly uploaded from Excel) or it's null (people never uploaded value from Excel to this project).

Any help is appreciated. Thank you.