// definition:
Call<ContextDto> ContextCall = _contextService.getContext(MinesiteID, lastModified == null ? "" : lastModified, UUID);
// if the optinal paramters needs to work out by empty string, we can do some wrapper on it.
// we can pass the null. it should alwasys work out.
ContextDto contextDto = contextApi.Get(_minesiteID, Null, _uuid)