Have you processed your model or have your process null on the model.
If not , you could process the model see if any results get out and replace the "blank".
Is it showing blank because the measure will only display its value when used in ie PowerBI or is it that there is an issue with the measure itself? how can I test if it works?
No, it would give you same value, if all things went well. It is not only working in PBI. For example :