dataset create web-service requires id param, docs state this is an optional param

[lachlanhurst]

Documentation states a new dataset can be created without an id, yet calls to this webservice fail without this URL param.
https://github.com/VPAC/rsa/blob/master/doc/spatialcubeservice.md

Workaround is to include the id param in the URL with no value.
ie, make post with URL such as;

 http://localhost:8181/spatialcubeservice/Dataset.json?precision=1&dataAbstract=a&name=clientCreate1&resolution=m25&id=

Issue traced to line 108 of DatasetController. The if statement throws a null pointer exception as getId() returns null as the dataset does not exist (it can't as it is being created).

if(dr.getId().isEmpty()) {
        Dataset newDataset = new Dataset(dr.getName(), dr.getDataAbstract(), dr.getResolution(), precision);
        datasetDao.create(newDataset);
        model.addAttribute(ControllerHelper.RESPONSE_ROOT, new DatasetResponse(newDataset));