Custom Function doesn't add when other values are null

To create calculated columns that can be merged into other queries, I have to create a custom column within the Power Query Editor. When I type in my formula, it works until there is a null value. Normally, in SQL, this would just be read as something similar to a zero and the function would work fine. Instead, Power Bi refuses to conduct the calculation and inserts a null value into the calculated column when it is simple addition. Power Bi needs to be programed to recognize a null value as the equivalent as a zero when functions are being used.