Allow nullable primitive types, so they can be used as return type

#### Description:

As discussed in the Error Management Workshop ([notes here](https://burohappold.sharepoint.com/:w:/s/BHoM/EZ3I_cCKETdLuwNcWhz9sJgBbseWgOvxbKkQJ7tgayQ-og?e=m4JNUN)).

Nullable primitive types would allow for an additional mechanism for better error handling. Instead of returning a boolean or an empty data in case a method fails, we could return a null.