cdm/src/main/java/ucar/nc2/Group.java
public void setParentGroup(Group parent) {
    if (immutable) throw new IllegalStateException("Cant modify");
    super.setParentGroup(parent == null ? ncfile.getRootGroup() : parent);
  }
public void setParentGroup(Group parent) {
    if (immutable) throw new IllegalStateException("Cant modify");
    super.setParentGroup(parent == null ? ncfile.getRootGroup() : parent);
  }
Set the Group's parent Group

@param parent parent group.