For an application with lots of calculations I have a problem with the null values of decimals. When an input (Number) field is empty, i don't need the calculations to be run. But, OutSystems converts empty Decimals into 0. But, the number 0 should be a legit value.

Ok, so there's always the possibility to bind the input to a Text variable. In that case, you will need to perform validation yourself.

Another possibility is to fetch the input value in a Javascript block. Create a Javascript block with InputWidgetId as input, and TypedValue as output. Then write something like: