Fix a bug in OrganisationDTO(Organisation organisation) constructor.
this.parentID = organisation.getParentOrganisation().getOrganisationId() will throw a NullPointerException at runtime if the organisation is the top level organisation like "Root"
Now this line of code is modified like this:
this.parentID = (organsiation.getParentOrganisation()==null) ? new Integer(-1) : organisation.getParentOrganisation().getOrganisationId();
So in an organisationDTO, if parentID is -1, it means the organisation is the top level organisation which has no parent.