public String toDebugString() {
        return "UserRef{" +
               "uuid='" + uuid + '\'' +
               ", subjectId='" + subjectId + '\'' +
               ", displayName='" + displayName + '\'' +
               ", fullName='" + fullName + '\'' +
               ", group=" + group +
               ", enabled=" + enabled +
               '}';
    }
@return "Group" or "User" depending on type.
stroom-util-shared/src/main/java/stroom/util/shared/UserRef.java